secret door to an underground storm shelter/panic room/hid out in the kitchen island! Best secret passage ever! Definitely a dream home feature! (would also be good if someone broke into your house and you had to hide somewhere) Zombie apocalypse.
Built-in bunk beds is a great idea to preserve space. The built-in book shelves also help to create more storage for toys, books and etc. The first step of the ladder has been eliminated in order to add under bed storage/trundle.