A house with no windows...and no doors...
Only at first glance, and after that, you find out that there are more doors inside than you could ever imagine. Doorways inside of doorways inside of doorways. There's only one way out for any occupant - decide which door is the right one - and go through it. It could lead you to paradise...or into the depths of hell. It's up to you, so are you ready to go knock, knock, knocking...?