Be inspired by possibilities! Defeat the notion the stone interior walls are cold and dungeon-like. With the right designer/architect partnership they can be a fabulous signature in your home design.
I think for me it would be begin with an attraction to a stone's character and coloration. Then I'd find myself looking for a place for it inside. There have been stone that I loved but found it to be too much for the exterior of a home. Well, here's where you can have your cake and eat it too, so to say!
So many possibilities! An accent wall, a stairway enhancement, a room divider!
Played right and interior stonework could be part of what makes your bath more spa-like.
Loving this "tucked-away" wine cellar!
Image Sources: Eldorado Stone, Anne Decker Architects, Elle Decor, Pinterest, Locaita Architects, ADMagazine.FR, Facsada, Zsa Zsa Bellagio