For the basement stairs: cabinets, stairs with flip up steps and very narrow stairs. Each step goes up one at a time for each foot. It is sort of spaced so you are putting one foot per step with a steeper step. Very space-saving.
Attic Bedroom Closet Design, Pictures, Remodel, Decor and Ideas - page 9 - sublime-decor. I have the perfect wall (with attic behind it) to do this. I've often thought of making an easily accessible closet there.