The Osthofentor in Soest, our district town, is a former city gate, built with local greenish sandstone (aka "Anröchter Sandstein") in the period from 1523 to 1526. The gate is the only one remaining of the ten that guarded the old Hanseatic city. It now houses a museum of municipal history, and has a collection of 25,000 medieval crossbow bolts.
That "hole in the wall" is the gate's toilet, the English term for a medieval or Renaissance toilet and/or for a close stool is "garderobe" I've just learnt.