Though not much is known about the world in which The Last Guardian is set, much can be discerned from what remains of the crumbling ruins and from the geography itself.
A place shrouded in mystery, and for good reason. The Nest is comprised of a massive, crater-like valley surrounded by sheer, impassable mountain walls that can only be bypassed by air. Most of the Nest's interior is filled with crumbling castle ruins with towers, courtyards, bridges, passageways and temples. Underneath the surface are endless tunnels, some of them flooded, others barred by huge rusting gates of iron. Overall, the buildings and stonework are heavily overgrown with lush, green ivy, as well as trees and other plant life. No one knows who built all the castles, who may have lived here before, or what happened to these masters of architecture.
Something notable about these ruins is that they are covered in runes and carvings, some of which resemble the runes of the Master of The Valley. As before mentioned, it is unknown whether the Master's runes are connected with the construction of the ruins or not.
The ruler of this picturesque, crumbling landscape is an evil being known only as the Master of the Valley. It controls all the inhabitants. Amongst its servants are the Tricos, huge, winged griffin-like beasts and an army of possessed, living suits of armor called the Armored Knights. Only the Tricos can leave the Nest to do the Master's bidding as they possess the ability to fly. Other inhabitants include unknown species of birds, salamanders and butterflies.
The Outside World
Little is seen of the world outside the Nest. From breif glimpses, however, it seems to be heavily wooded as far as the eye can see, with a temperate climate. Rain and lightning storms appear to be just as common as they are in the real world.
Dotting the forest are man-made clearings containging human villages. The layout of these villages seem to mainly consist of a wide-open clearing with houses and other structures hugging the treeline. The technology-level of the human inhabitants appears basic, although perfectly adequate for their lifestyle: homes are lit with oil-lamps whille outside spaces are lit with torches; weapons consist of throwing-spears, bows and swords; armor may be sophisticated, but from what has been revealed of village defense--men waking bleary-eyed to fend off a beast with no time to put on armor--it is uncertian.
Little is seen of the local wildlife, but it may be fairly diverse, given the vibrantly green environment.