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
This is a perfect combo of my two favorite ideas for that space under the stairs leading to the basement. A reading nook AND book storage and shelves . assuming that there is enough space for this there.