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.
Ferrara Natural Travertine with Natural Chocolate Marble & Glass Mosaic Tiles. Using the marble & glass tiles along with the travertine adds a burst of glamour into your walls whilst keeping to luxury natural materials. This look is great as a splash back