Piranesi

I always include major spoilers (hidden), to help with my memory  issues. Read them at your peril! 

Piranesi lives in a fantastical underground world. He doesn't know that he has forgotten what has happened to him in the past. He trusts the only other person that enters his world, and he shouldn't. The story is strikingly original and beautifully written. The end of the story is a bit of a let down as he escapes into the real world above ground .