The reason it's best not to know much about this book is because it's like a puzzle game. The events and setting are kind of surreal and don't immediately make sense, and it's a lot of fun to be constantly thinking about possible hows and whys of everything.

I read White Cat, Black Dog by Kelly Link about the same time I read Piranesi, and I think they go well together as surreal fiction which is neither "lol random xD" nor pretentious.