A secret storage in a staircase can be a great hidden storage for bulky things that look unflattering when stored in full display. It’s the same space under stairs only hidden and accessed from the floor in the staircase. At: The Bottom Of The Stairs
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Creative ideas for using the space under the stairs. Brilliant use of space! Not nuts about the bathroom idea though. I guess if you had a tiny home with no main floor powder room it could be workable.