When you see how The Last Guardian's environments fit together, it all makes sense
The Last Guardian takes place in one interconnected environment, and it's possible to trace your journey from start to finish once you see the whole thing.
The Last Guardian is set in a strange crater-like area described in-game as a valley. Referred to as the Nest, it's filled with mysterious crumbling ruins, the purpose of which don't ever really become clear - although I certainly have my theories.
The environments are really important to The Last Guardian because it's a traversal puzzle game - almost all the challenges you face are a matter of figuring out where to go, and then how to get there despite the obstacles in your way. (If you're having troubles with any of them, check out our The Last Guardian guide and walkthrough).
As such, Team Ico could have been forgiven for relying on unreal architecture to string the puzzles of The Last Guardian together in a way that isn't possible in the real world. But in fact, it looks like the Nest can actually be rendered as one continuous bit of geometry.
You can see the whole of the Nest ruins at one point late in The Last Guardian, and as spotted by Polygon, Redditor CandykillerArt put together an enhanced image showing off that view in a way that makes it easier to see and identify various areas you will have visited on your journey.
In reaction, lyraa3 went over the map and labelled it so you can more easily pick out what corresponds to which area of The Last Guardian. That image is embedded above, but you can hit the earlier link to see the clean shot if you prefer.
It looks even more complicated now, honestly, and I'm really glad seeing it this way hasn't dispelled the mystery. The Last Guardian was one of my favourite games of 2016, and I expect we'll see a wave of pets named Trico over the next few years.