By a certain age, kids long for a secret hideout, a place all their own to play and imagine. If you want to create such a space in your home, there are tons of options - temporary forts made from sheets, teepees, tents, playhouses, clubhouses and treehouses. For the architecturally blessed, there is this.
This modern home features a secret playroom above the bedroom accessible via a climbing wall. The space above is tall enough to sit comfortably and stand carefully. It's probably not the most practical for cleaning purposes but it is pretty nifty. If you're curious about the rest of this home, check out the slideshow on Dwell.