Stash Cash in the Door? - 15 Secret Hiding Places That Will Fool Even the Smartest Burglar. you know until you put it all over the Internet and then everyone and their mother knows you have secret hiding places.
The hammock is a great idea so smaller "secret playroom" areas. This kid’s bookshelf opens to a secret reading nook. A SECRET READING NOOK. I would’ve never left. (from Everything About Secret Bookcase Doors)
25 astuces géniales que tous les parents paresseux doivent connaître
// This rotating bird feeder brings birds into your home for warmth and observation during the winter. Even better, a mirror prevents the birds from knowing you're watching them, so they don't get frightened!
So much room for activities. but little, individual reading/working nooks (for a tea house or library.) -- or just a space to crash/decompress/work in a different position. And the scene from step brothers makes it even better!