I thought I& already found the best example of a BILLY hack already —these built-ins from Gwen of Makerista, which we posted early last year. Then this project came to my attention, and I& made room in my heart for two loves instead of just one.
This could work in a tiny bathroom. Love the tiled floor/painted wall combo and the fact that the tiles in the shower match the wall colour but are different from the floor. The niche for storage works well for us too.