Under the Stairs - Smart Storage - 16 "Sneaky" Ideas - Bob Vila - Staircases take up a lot of room. Where square footage is precious, use custom-fit cabinets, drawers, and closets with clever pullout drawers to make full use of the under-stairs space.
17+ Unique and Stylish CD and DVD Storage Ideas For Small Spaces
Levitate Architects used a staircase to a loft-like bedroom to create an enormous amount of book storage space. Even though the staircase isn't very compact but could accomodate so many books that it would save some space anyway.