Large rustic stone shower for the cabin.plus you don't have to go through the hassle of cleaning a glass door. Okay, I don't want it this rustic, but this would be idea for the bunk room bathroom, and you could put shower heads in it.
Okay, I know this is a spa and not a house. But if there was a "waterfall" in my house, with a small pool to hang out in, in a room with tons of natural light, and all that good stuff.I would never leave my house.
Dream Shower - Shower with heated floors YES to heated floors, slab stone (instead of tile/grout), real-sized bench. ADD: steam shower and LOTS more built-in niches for essential shower supplies. Probably a different stone.