Laying river rocks as the floor tile in a shower gives the shower a unique, nature-like appearance while providing you with a standing surface that massages your feet as you shower. Install the rocks with a standard white mortar to create a white edging around each stone, or place the river rocks in a bed of clear epoxy to make the stones appear as if they're resting in a bed of water. In either case, allow at most half of the rocks to protrude past the binding material, even if just a little. If you use clear epoxy, you have the freedom to place rocks below the surface of the epoxy so you see them but don't feel them.
Install river rocks into a counter top using one of the methods you'd use to install the stones into a shower floor. Consider covering the counter top with a glass surface and sink if you want the rocks to protrude past the binding material, because the uneven counter top makes it difficult to balance items on it. If you prefer to have a counter top with the uneven stone surface, still consider using a clear sink so you can see rocks through the sink and the sink doesn't interfere with the stone design. Use river stones sunk entirely into clear epoxy for a flat counter surface you don't have to cover.
A river rock floor mat is a simple way to incorporate river stones into your bathroom design without any remodeling or heavy construction. Purchase a river stone bath mat, available in different stone colors and sizes, at a home and bathroom decoration supply store. Place the mat directly outside the bathtub or shower, or in front of a vanity so you can stand on it while you conduct your daily hygiene routine.