Bathroom Spa Murals or for a powder room create a huge effect as they will create an optical illusion. They make a long or small bathroom look bigger.
Of course you can use wall paper but keep in mind that if you want to remodel you must remove the wall paper first from the walls.
A structured wall finish can also be a solution. The orchid mural below had been painted on a wall finish.
The photos below show bathroom murals, a French country wall finish with matching doors and window frames, a orchid mural, and a stenciled romantic design for a lilac bathroom (very shabby chic).