The First Age of Cthon (at least, the first one to be recorded), was a world in which Life and Chaos dominated everything, with results that are utterly alien by later mortal standards. The proof of this is that the obscure and inhuman intelligent races of those times, later surviving in the Underdark, Abyss, and the other dark pieces of First Age that went underground, have such distorted morals, logic, and ideas because they are in tune with that world. A world that, fortunately for humans and demi-humans, practically auto-exiled itself, leaving place for a new world on the surface of the earth.
That new world is what later sages refer to as the Second Age World, sometimes also referred to as the "Golden Age".
The World of the Second Age
The incredible disaster that ended the First Age World literally ripped the earth and sky apart.
Immense volcanoes erected themsleves in a single, apocalyptic, and endless night. Lava erupted from them copiously, like blood gushing messily from dire wounds. The wounds which the very earth had been inflicted by the warring Elder Gods. Rain was like entire seas dropped from the sky, and waves were as tall as mountains.
The whole surface of the world was reshaped, even if for some obscure reason, many places survived, encased by the newly formed rocks as if some kind of invisible shield had protected them from the elements. Even like this, those places were now sealed by unthinkable amounts of solid rock, and the surface of the world was virgin, untouched.
During the earth-shaking disaster though, something incredible had happened, which gave to the new virgin world a new generation of powerful beings: the very elements that obliterated the First Age World had become sentient. And it wasn't a mortal kind of sentience: they were true gods.
This new generation of gods, called Titan Gods or Primordial Gods, was completely different from the first generation, the chaotic Elder Gods. Some laws, a universal order, were clearly at work in the rising of these new gods. Not a single one of them was without a clear function or logic, a strong identity, something that mortals could relate to. And all of them in some way represented both living and inanimate aspects of the world which were in some way "violated" by the excesses of the First Age.
I will deal with these gods later. Only thing to be taken in consideration in talking of the Second Age World, is that these gods were sometimes forces of order, sometimes of chaos, but always forces of creation. Destruction, which the Elder Gods craved so much, wasn't an interest of these new gods if not in brief moments of anger. These new gods knew for the first time in their vast souls a cosmic force that never before had touched mortal or immortal being of sort: love. These gods loved their creations and the beings that venerated them, and they helped these beings and creations all the time, although not often first-handedly.
The physical world of the Second Age.
If from a quantitative point of view, Life had taken a hit in the passage from the First to the Second Age, from a qualitative point of view (at least a mortal one), Life was finally allowed to blossom in beauty. No written or spoken words from the Second Age forgets to describe how beautiful the world was. If living things were smaller in scale compared to the First Age, most of the flora was still gigantic compared to that of the Third Age. Trees in particular were colossal, but never looking out of place or out of control. Temperature was cooler and humidity lower and more variable in most of the places of the earth, so the chaotic and immense jungles of the First Age were a rarity instead of the norm. It was like nature had finally found a point of balance between size and order, beauty and wilderness.
Following this new order, the thick forests didn't cover the whole surface of the world, but they concentrated into clearly defined regions, leaving space to peaceful prairies, low density woodlands, naked hills and mountains, and lots of glaciers too. The North and South of the world were dominated by ice and tundras, but even there, the strong new fauna and intelligent races of the Second Age World managed to live long lives. Because again, whereas in the First Age life was incredibly ubiquitous but short, in the Second Age it was much more confined, but also much longer, especially for the mortals. Never in the history of the world did mortals live as long as in the Second Age.
The races of the Second Age.
Many of the intelligent races of the Second Age also existed, in more primitive forms, in the First Age, although nobody can tell for sure. In fact, it is not clear if the scarce words dedicated to the First Age and written in the Second came from direct experience or perhaps contacts with the few survivors of those ancient and inhuman dominating cultures. Or perhaps from wild imagination even. But in any case, there were only two possibilities for the new races of the Second Age: they were either created directly by the Titan and Primordial Gods, or they had evolved in time from more primitive ancestors survived from the First Age. Even within the same culture, legends sometimes talked about both possibilities.
The first intelligent race to emerge, or at least the first to leave trace of its passage, was that of the dwarves. Elves were probably contemporary, because among the first records of the dwarves, there is talk of the elves, the name of which coming in fact from dwarven runic language (while elves have names for their very race(s) that sound differently). The dwarves often occupied the places in which the powers of the elements were stronger. Especially the elemental Earth. They became the first to understand how to work metal and gems, and every gift embedded in the rocks. It is not clear if dwarves were actually created by an Earth Primordial or were simply elected by one or more of them as favorite race, but their association with the god of elemental Earth, whom they called Moradin, and some other similar godly beings, is a fact.
The elves, which consider themselves the first race to have spoken a language (although proof is scarce, rightly because of their stronger interest for the spoken word, compared to the written one), were instead drawn to the natural gifts of the forests and every living thing. Again, the nature of their link with the Forest Gods is not known for sure, but the association is even stronger than that of dwarves, because it is all to clear for the sages of the Third Age, that elves became in some way capable of physically inhabiting the very dreams of the Forest Gods, dreams made real, in the form of a wonderful world out of space and overlapping with the material one, named Feywild or Faerie.
Elves and dwarves dominated the Second Age, culturally speaking, but even combined, their numbers were not as great as those of humans. Humans were much more primitive, with only very few living in cities built by themselves (or more often abandoned by some other race), and only few of those having discovered writing.
More races were born or at least first-recorded in the Second Age, races like gnomes, the various wee folks, halflings, goliaths, tritons, and in remote places even dragonborn, orcs, goblins, and various beast-men. Many of these produced shining cultures that survived as awe-inspiring ruins in the Third Age. But more than any other race, dwarves, elves, and humans played protgonist roles in the Second Age, and for a very long time living in peace and harmony.
Magic in the Second Age.
The very nature of the Primordial and Titan Gods was magical, and as such, the first forms of ordered magic were born in the Second Age among the mortals. Elemental magic and Sorcery (the first Arcane magic, but different from Wizardry) appeared where the gods and the dragons mingled with mortals. Only those with elemental or godly (titanic) blood could use this powerful magic, so Sorcerers and Elementalists (which some say are two names for the same thing) were few and well known. They were often the mightiest heroes, but also sometimes the most dangerous villains.
Primal magic was the province of the Elves and the other fey creatures that venerated the Forest Gods, but it became more widespread than its primitive form during the First Age. Basically every community of intelligent beings had a shaman, druid, or magic user of sorts expert in Primal magic, and sages think it was the magic that defined the Second Age, in many ways, and probably one of the forces responsible for the Second Age beauty and long lasting centuries and millennia. In some way, it was also the equivalent of divine magic, in that Primordials and Titans were gods deeply in tune with the environment, and as such masters of Primal magic.
A distinction made by Third Age sages classifies the Second Age Gods more associated with Primal Magic as Primordials, while those more associated with Sorcery/Elementalism as Titans. It is a rationalistic classification typical of the Third Age academic thought, which might bear some truth but is mostly a generalization that doesn't mirror the more organic reality of the Second Age gods.
Form of Witchract and Eldricth Magic (the magic of Warlocks) were still also abundant, especially in the many uncivilized places were the new gods were felt as distant (since they were drawn to more civilized mortals). In these places, humans and other mortals sometimes turned their faith towards surviving Elder Gods, which living underground or under the sea, sometimes gave to their new worshipers very immediate and well-liked boons such as exceptional fertility of the earth or abundance of fish. At dire prices of course, not easily seen by the mortals until it was too late...
Not only Elder Gods, but also some new beings from the underground, connected with death and the most terrible emotions and concepts, granted boons to those that stroke bargains with them. These obscure beings are classified in many different ways by Thrid Age sages, but nobody is really sure about their nature, not even if they all belonged to the same category of beings. Some ancient language refers to them as Yugoloths, some other translated to a generic "devils", that some sages took for the specfic Devils known in the Third Age. Others think they were just the demons of the First Age that, filled to the brim with anger and vengeful purposes, digged their way up from their Abyss deep underground.
Some far flung cultures, often very distant from the physical domains of the Titan and Primordial Gods, also re-discovered Psionic, for the first time after the end of the First Age.
All in all, practically every form of magic was present in the Second Age, save for sensu-strictu Divine Magic and Wizardry, the first because it is directly connected to the Celestial Gods of the Third Age, the second because it required an understanding of Sorcery so complete, that it took many bloodlines of sorcerers and the entire length of the Second Age to be mastered, it is said by elves and/or humans. And when it was finally mastered, it is also said that wizardry was one of the true causes of the end of the Second Age.
The end of the Second Age.
The Second Age consisted mostly of millennia of harmony and peace, only briefly interrupted here and there by small scale wars and skirmishes between civilized and barbaric mortals, monster hunts, baccanals, and the occasional clashed among the Titans and Primordials and between them and surfacing Elder Gods or their spawn.
But for some obscure reason, the last years of the Second Age were woeful strikes that tainted its "golden" nature and climaxed into another world-wide catastrophe.
Dwarves and elves respectively blame one another for the disaster. Elves talk of how dwarves would have "violated Mother Earth" with their endless digging, which went to deep, uncovering some ancient evil. Dwarves speak of how the elven witches, in their blaspheme decoding of sorcery into wizardry, allowed for spells far too powerful to come into being, breaking the laws of the gods and ultimately breaking the Earth itself.
It must also be said that those last years were marked by the first and last bitter war between Dwarves and Elves, but that alone could not have caused the Great Disaster, and similarly, an Elder God or two that the Dwarves might have released by digging, or some Elven High Magic would not have been enough. Not by themselves. The truth must be that the combination of these and other accidents might have been more lethal than the sum of its parts.
Even the more primitive humans had reached dangerous heights that some say could have lead to disaster, in those last years of the Second Age. A vast empire occupied a big portion of the known world, and its alliance with dragons and the consequently large number of Elementalis and Sorcerers was surely an explosive mix.
Another very important factor, the new Celestial Gods were born sometime before, or during the Great Disaster that ended the Second Age. It is really unclear how and why these new gods were born, and what role could they have had in the end of the age.
What is sure is that all of these very different events have one thing in common: a push towards rationality. The growing "technology" of the dwarves. The expansion and taming of the elements of humans. The discovery and abuse of "rational magic" of the elves. And ultimately the rise of the Celestial Gods, which could be described as rationality made divine. In some way, this mixture of things that challenged the natural harmony of the world, ended up destroying it. Or better yet, reorganizing it, ironically not in the most rational way at all.
The Great Disaster basically razed down all civilizations and re-arranged the world in incomprehensible ways. Magic was imbued into many places, and Life again took a hit, this time not for the better, touching all new lows in the Third Age.
Planar features, and the Second Age after its end.
The Second Age World saw the modification of one of the parallel "places out of space" of the world, and the appearance of a second one. Both survived into the Third Age, although not unscathed!
The "Shadow Web" becomes Hades. (Also, Elysium)
For some reason, the Shadow Web "plane", which nobody knows exactly what form could have had during the FIrst Age, except for a few hints that seem to place it "in the sky", physically "fell down" into the earth, just like every other part of the First Age physical world.
However, be it different from its first incarnation or not, it surely differed from its latest during the Third Age, in which it truly became a "web". During the Second Age, it seemingly was a much simpler place, that did not connect many parts of the world and the underworld, but simply stayed between one and the other. A few physical points of entrance existed too, and they were not necessarily connected with pure darkness, although they were dark in other senses, for sure.
This place was called Hades, and it became the resting place of the souls of the dead.
One of the Primordial Gods, the one associated with Death of course, makes of Hades his home, and by some cultures is himself called Hades.
Note that not all the souls reach Hades to stay. Some can be brought back into life, others go to another place entirely, called Elysium by the same cultures that recognize the name Hades (other cultures had different names for each). It is said that this place exists in the world, on top of an enormous plateau, in an unknown land beyond the greatest ocean.
So what kind of souls go to Hades? Usually the ones that left something "undone" in the material world. Which means the vast majority. But Hades is not a place of suffering, just of rest, if a bit sad. After all, life was supposed to be better in the Second Age, so death is rarely seen as something "beatific" as in the Third Age. Instead, it was just a matter of the emotions at death time. Elysium or its equivalent is for the few mortals, mostly warriors, who had died very gloriously and without regrets. What becomes of them is not known because while Hades can be visited by mortals, there are no records of mortals visiting Elysium.
The vast majority of souls went to Hades though, where some souls, usually the ones more desperate or with more unfinished business, are contacted by beings of various names, which have some interest in making the dead soul even more desperate, by tempting it into recalling all the worst aspects of their unfinished businesses in life. Seemingly getting nourishment from the profusion of ill emotions, these beings seemingly acquire the ability to exit the netherworld and go haunt the living. These creatures apparently started by (righteously or not) avenging the desperate soul that triggered them, but then fly into a rampage, perhaps avenging all the similar slights or crimes, even if much less severe, or maybe striking down a whole bloodline or a whole village of mortals. The same dominating human cuture that named Hades and Elysium with these names, also called these beings "the Furies", classifying them as "Daemons", but after receiving information from documents of other cultures and apparently from the netherworld itself, Third Age scholars have come to call them Yugoloths.
The origin of these beings is a mystery. In particular, it is not clear if they're connected to Hades/Shadow, with demons, or with the Primordial Gods themselves. The first two theories could trace back their origin to the First Age, perhaps as undead demons of the First Age, or the original inhabitants of the First Shadow Web; the latter option would instead mean that some Primordial Gods were born connected to negative concepts and became these Furies, or perhaps that these beings are rejected offspring of Primordial Gods with either mortals or more powerful creatures. Some say that they are connected with the God of Hades himself, since he is already much more ethereal and negative compared to his kin, making him the God closest in nature to these evil beings.
What is sure is that during the Third Age, in which Hades is no more, these creatures dwell in a deeper and less known place of the Underworld called Gehenna. From here, not having access to the souls of the dead that nourished them with their desperation, they became mercenaries to any being that could offer the same emotion in some form or another. Ultimately, their purpose seems to just feed on negativity to spread even more negativity. Not plain destruction like demons, not pure corruption like the later devils, but something equally evil.
The dream-world of the Forest Gods: the Feywild.
Most of the Second Age Gods, especially those more connected with material elements and classified by later scholars as the true Titan Gods were not very dreamy beings. They lived in their eternal "now", without needing to imagine nothing but the shape they wanted to give to their present moment. But some others, those that the stricter classifications call as the true Primordials among the Second Age gods, thus the ones connected with elements "less material", such as Life, had a more complex mind, reflecting the complexity of their associated element. With these complex minds, they always dreamed, not even needing to sleep to do so, being gods. The dreams of these gods, usually referred to as the Forest Gods, were so powerful that they transformed into real world, although disconnected from the reality of the material world. They draped the material world like thin veils, and in some points, and especially only for selected individuals or races, the veil could be pierced and this dreamy world explored as a substitution of the material one, without perceiving any difference in its nature, except for its incredible beauty.
What could a Forest God dream? Of course, it would dream of forests. Perfect forests, like not even the majestic Second Age forests could ever be. In a way, the Feywild, also called Faerie, was similar to a beautiful version of the First Age World, in that there was much more life into it, but instead of being completely harmful to normal mortals, it was life that made the world even more inviting, although not devoid of danger.
The elves and countless other minor races that lived in harmony with nature (often directly linked to the Forest Gods themselves, sometimes being direct offspring) made the Feywild their home, sometimes disappearing from the material world completely, never to return until the Great Disaster hit the Feywild too, between the Second and Third Age.
The Second Age World in the Third Age.
The Great Disaster that triggered the Third Age was in some ways less physically world-shaking compared to the First Disaster. After all, most of the casualties among the mortals (and the Titans/Primordials) were linked with the wars that predated the catastrophe, and not the catastrophe itself.
So it was more of a magical disaster. Magic itself changed, stopped functioning for a while, especially Primal Magic, and many places of the world shifted in space as if teleported, without leaving trace of their monumental "voyages". One of the few things described factually by Third Age scholars, the Great Disaster in some way "tore the fabric of reality".
Even as such, most of the Second Age World remained where it was, but was simply abandoned due to migration, loss of culture, or more mysterious disappearance of the population. The surface of the world remained more or less the same, although ancient maps from the Second Age still don't lead usefully in the Third Age.
In any case, the Second Age World in the Third Age is mostly composed by ruins, plain and simple.
The direst effects were felt in the Feywild, in which the magical effects were amplified, the Shadow Web, which actually became a web due to the catastrophe, and began conecting very far places and hiding in its pockets and folds places from all the three ages, and finally in the portions of First Age World, which too often became much closer to the surface.
The most beautiful effects, although worrying for some minds, were the portions of earth (often including ruins) that began to float in the sky. A very selected few of these were present in the Second Age, but were reserved for the Sky Titans, but for some reason, the Great Disaster made the phenomenon more common, and even places of the Underdark became like floating islands in the Third Age.
The Dark Age, name given to the first hundreds, perhaps thousands of years of the Third Age, filled the mortals with so much fear and superstition, that even in the most recent times of the Third Age when civilization seems to be advancing again, the floating islands, the ruins, the endless mountain halls of the dwarves and the entraces to the faerie realms are places that are avoided by mortals at all costs, sometimes even denied and forgotten. After all, the most prominent and mobile of these features, the floating islands, are still not very mobile at all, and also tend to be concentrated where the other features from the Second Age are situated, and in places of arcane power, in which the forces of the Great Disaster never ceased to be at work. Because of this fact, and the fact that humanity and most of the other mortal races began to fear the unknown more than anything else, civilization migrated quite as far as possible from these "excessive wonders", and with time, they were all but forgotten.
Only the less rhetoric and secularized among the scholars, and the bravest and craziest adventurers of the Third Age eventually started to explore these places. Unknowingly, they were often escaping worse destinies, since the brutal realities of the First Age world and the new dangers posed by the arrival of devils, where often much nearer to the ignorant civilization of the First Age than the much feared ruins of the Second Age World.