Go into the bathroom and turn on the shower. First of all, does the water flow, and does it get hot and cold? Does the water look less than clear in any way? Look at the walls of the shower to see if there are any missing or damaged tiles or if mold is present.
Check out the toilets. Are they clean, and do they flush properly? Do they run when they aren't in use? Make sure the toilet doesn't leak onto the surrounding floor, too.
Take a look at the sinks. Check to see if the faucets run hot and cold here as well, and that water drains properly. Note any damage to the faucets or the porcelain. Also, be sure to check the cabinet under the sink to note any leaky water, mold or strange smells.