built-in bunk / loft. I can visualize this as a larger studio apartment for an adult, with a home office (or a storage area) above the bed. Pull the doors shut during the day and the bed will disappear, and the office will have a loft-like appearance.
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!