I had an incident like that last week. I put DS down for a nap and 20 minutes later opened the door to check on him. I about panicked when I couldn't find him at first. Finally I walk into his room and I discovered him napping on top of his changing table! Very quietly, I left the room, retrieved my camera, took a picture of him and then returned him to his bed. I don't want to know how he got up there.