What's on the other/back side of the wall where the faucet is located?

Unfortunately, there is a corner shower on the back side of the wall in the
other bathroom. So no access from the back, even if I wanted to tear into
it (which I don't).

Her house is two hours away from me. We're busy moving her to an assisted
living home, so I don't have the time or money to invest in major repairs.
Just trying to fix anything small that we can before we try selling it.

Anthony