A bed tucked under 'trap doors' in the floor - makes for a flat play area during the day! (Kids' Playroom Design Ideas : Rooms : Home & Garden Television)
Also on these boards
Fun in the Forest - 21 Amazing Rooms That Make Us Wish We Were Kids Again on HGTV
Clever place to hide a bed. This is sooo cool. I need this!
Amazing Kids Rooms - Gallery of Amazing Kids Bedrooms and Playrooms : Rooms : Home & Garden Television