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.
Trendy Good Ideas / Staircase = In this under stair storage solution, a door opens and reveals a series of drawers; they provide plenty of storage space, all hidden behind this secret door. It’s a clever solution for hallways.
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.