Though little is known about the world in which The Last Guardian is set, much can be discerned about it from what remains of the crumbling ruins and from its respective geography.
A place shrouded in mystery. The Nest is a massive, crater-like valley which can only be accessed via flight, its sheer, cliff-like walls offering no routes to take by foot. Crumbling towers, courtyards, bridges, tunnels and temples lay in uninhabited decay, giving the bowels of this valley a formidable and lonely atmosphere.
The main complex stands isolated in the valley's center, each temple only connected to another via cliffside paths and bridges. Getting between these buildings proves difficult as, any man-made structure has fallen prey to the elements and is ready to collapse at any moment; Trico's size and weight add further trouble. Once inside these buldings, however, the walls and foundations are solid. Endless, winding tunnels—some of them flooded—make for puzzling situations.
The buildings and stonework are heavily overgrown by lush, green ivy, sections of forest, and other lesser plant life such as moss and lichen. It is unknown who constructed these ruins, who may have lived here before or, what may have happened to cause their downfall. It is highly likely that the Master of the Valley was responsible for the Nest’s current dilapidation, although this is uncertain.
The carvings and runes coating these ancient structures can offer insight into the Nest’s history; their overall shape, style, and design highly resemble, if not match, those of the Master of The Valley. One theory is that these runes were implemented by the Master and, if so, it might have been responsible for the ruins’ construction. Another theory is that the people who built these ruins happened to share a common language with the Master. In this case, the Master’s involvement is indiscernible.
As the ruins are uninhabited by any known civilization, animals and other beings have taken up residence. These creatures include griffin-like Beasts, an army of hollow suits of armor, small birds, salamanders and blue butterflies. The most notable being of the Nest, however, is the Master of The Valley. It asserts dominance over the Beasts by controlling their actions. It is also responsible for animating the hundreds of suits of armor.
The only one of these inhabitants shown to be capable of leaving the Nest are the Trico-beasts. This is likely the reason why interaction between humans of the outside world and the Knights of the Nest has never occured within living memory. This is also probably why the Master's influence has not yet extended beyond the valley's high walls.
The outside world
Little is seen of the world outside the Nest. From brief glimpses, though, it seems to be heavily wooded as far as the eye can see, possessing 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 containing human villages. The primary layout of these villages seems to consist of a wide-open clearing with houses and other structures hugging the treeline. The technology of these human inhabitants appears basic but perfectly adequate for their lifestyle: homes are lit with oil lamps while outside spaces are lit with torches; weapons include throwing-spears, bows, arrows, and swords; armor may be sophisticated, but from what has been revealed of village defense—men waking bleary-eyed to fend off a beast—it is uncertain.
Little is seen of the local wildlife, though it may be fairly diverse, given the vibrantly green environment.