If the can-cave were completed, it would be a large windowless room but it would have a fake wall and fake windows that partition a smaller room; let me explain.
On one side of the room would be a bar, in the middle of the room would be game tables like pool table and football table. At the other end of the room would be fake windows with 4 recliner chairs, a roller blind would come down Infront of the fake windows and a projector would project a games console image onto the roller blind for the fake windows. Next to the fake windows would be a fake cupboard, it is actually a doorway to the room behind the fake windows. A metallic blue walled small room with 4 pods for walking in virtual reality and it would also have a single row of cinema seats so a group of people can watch a film projected on the wall.
The whole place is a little world with one extra rule, don't discuss the outside world. When you're in the happy zone the rest of the world doesn't exist. Just be a happy little kid for a little while.