[Image via ArchitectureMNP.]
There is a great post over at ArchitectureMNP showing a stair by the London based Levitate Architects that doubles as a giant bookcase. This is a great way of adapting a zone of typically dead space so that it can serve a dual purpose. I can imagine this would be really useful in some of the Washington, DC town houses that area really narrow and lacking in storage space. With a stair like this you would not need book cases, so wall space can instead be used for artwork and furniture.