The Ancient Builders
Ruins that can be found on the banks of the Great River fall into six different categories that each have their own typical traits, treasures they might contain, and dangers they pose.

Wilders
While the civilizations on the coast are still quite young, the ancestors of their people have been around for a very long time before that, always roaming deep in the forests and mountains and hiding from site as the great civilizations of the river valleys came and went. Many such tribes still exist and they might be as numerous as the city people, though spread out over much vaster areas, in terrain that takes much longer to cross than sailing up and down the coasts. These people are now called the Wilders by the city people, but not that long they all used to be the same.
Wilder sites are most commonly found in natural caves, but more recent ones also exist within ruins of the ancient civilizations which have lain abandoned since the Naga retreated further south. They are rarely dangerous in themselves, as Wilder traps made from wood don't last long, and they have few magical creations that could be a real threat. The greatest danger in Wilder sites comes from whatever might be making its lair inside them now. There generally is little gold and silver to be found in them, though they can hold various minor magic items that were taken from other ruins and given as offerings to the spirits or grave goods for dead heroes,.Wilder shrines are also often found at magical springs or other sites of supernatural power.

Naga
The Naga were the last civilization that controlled the Lower River and the Black River and they
eft behind numerous cities, palaces, and castles, which are often still quite well preserved. They held large numbers of mortal slaves, from which knowledge about the serpent language has been passed down among the Wilders in the area through the ages, which laid the foundation for the current civilizations. But the dewllings of the slaves have decayed long ago, leaving only the great stone buildings of the Naga masters behind. Many still have objects made from treated wood that have lasted through the centuries, though they usually have started to fall apart for a good while now.
Having never been looted yet, Naga ruins often have considerable amounts of gold and silver left behind. While for whatever reason the Naga did not take all their riches with them, they left a lot less beind in magic items, though those can still be found in Naga tombs.

Tower Builders
The Tower Builders were a mysterious civilization that preceeded the arrival of the Naga in more northern lands but existed alongside them for a very long time and only fully disappeared not long before the Naga began to retreat south themselves. The Towet Builders were asura, a race of humanoid people whose origin lies with the demons of the Underworld. Though they are mostly humanoid in appearance, their minds are nearly as alien as those of any demon. Asura are rarely seen in Kaendor, but the sheer amount of ruins they have left behind throughout all known corners of the world indicates that they must once have been a much more numerous civilization.
Tower Builder ruins are easily recognized by the great numbers of large towers they include, but they are not the only type of buildings they made. These towers are always square in shape, getting narrower towards the top, which takes the form of a flat tarrace. These ruins are build from very large stone blocks of a sheer endless number of irregular shapes that are fitted together very tightly and have proven to be extremely stable even in earthquakes. Tower Builder ruins on the Lower River and on the lower Green River close to Lake Amara have often been plundered by Naga many ages ago, and moat valuables that can be found there have ended up there more recently or were only uncovered as the old towers started to crumble. But ruins further north can often be found seemingly untouched through the entire length of the Naga reign.

Tree Weavers
While the Tower Builders are mysterious, barely anything about the Tree Weavers is known.Their ruins are quite, and often describing them as ruins doesn't seem to be the right term. The Tree Weavers had an art to weave together the branches of trees and make them grow together into solid walls and floors with doorways, windows, and staircases. A process that must have taken centuries, even with magic. Some of these sites have fully or partially died over the ages and gradually started to rot and crumble, but many still continue to grow and have reached enormous heights. This also makes it impossible to tell how long ago they might haave lived, but it is clear that no new ones have been made for many centuries. The scale of many Tree Weaver ruins indicates that they were probably humanoid in shape and of similar size to Naga and asura, but even that is only speculation.
There are rarely any coins found in these places, but many are grown around powerful supernatural sites or are home to many different spirits of tbe forests.

Rock Carvers
The Rock Carvers are one of the oldest civilizations that came long before the Tower Builders. They created their cities and steongholds almost entirely without using masonry snd instead carved them as solid single pieces out of the rock of mountains and cliffs. This unique and certainly slow method of construction also made them extremely durable and many are still innamazing shape. Despite the imcredible age if these ruins, their creators are known to have been giants, 3 meter tall humanoids who often possesses various magical powers. The giants claim that the Rock Carvers where their distant ancestors, but also seem to know very little else about them. But given the abundance of these ruins, their people must once have been much larger in number.
Rock Carver ruins are extremely strong and breaking through sealed passages is extremely slow and difficult, if not even just outright impossible. But this trait also means that many ancient vaults and hoards have remained untouched for several thousands if years, their protections only defeated evwntually by errosion and earthquakes. As the mountains themselves begin to topple with age, these ancient barriers are finally giving up the treasures and secrets that they hold. Rock Carver ruins are attractive lairs for all maners of subterranean creatures, and they are often filled with dangerous mechanical traps, that sometimes become even more dangerous in their gradually collapsing state. One thing always highly looked for in Rock Carver ruins are steel blades. A secret the giants have closely guarded until this very day.

Glass Makers
Long before the Rock Carvers where the Glass Makers.The ruins they have left behind all over Kaendor are more strange and mysterious than any other. They appear to be made of a dark green glass that is extrmely strong and nearly indestructable. For a long time there have been stories of people seeing cracks in them which appear to have completely vanished when others explored the sites many years later. Glass Maker ruins are most commonly found underground, often beneath the ruins of other civilizatuons that seem to have build their own castles deliberately on top of them. There are however also a smaller number of strange great towers that rise out of tbe ground and far above the surrounding trees. The identity of the Glass Makers is completely unknown, but they don't appear to have been humanoid at all.
Glass Maker ruins can hold the most wondrous and often very powerful magic items, but slso dangers. Most of them have at least some water flowing through them, but many are also nearly completely flooded and home to many aquatic cave creaturs.