I have a leaky shower faucet. For fun, the previous owner walled over the access hatch to the plumbing and then put in a built in shelf in front of that. Yes of course the shelf is completely packed with crap.
Discussion
Is it common for showers to have a plumbing access hatch? Don't think I've ever seen that. Just solid tile the whole way around.
Supposed to be shutoffs on both hot and cold right before the mixing valve you use to take a shower or bath. There should be an access to those valves and the back of the knobs you use to take a shower.
They aren't in the shower because leaks. The access should be on the other side of the wall.
It is a smart move if you dont have one to allow for repairs vs ripping out drywall and having water damage. Unsure if bldg code requires it though.