Row after row after row in sets of 4 probably prefab concrete boxes, this beach operator has them numbered 1 through 54, building=changing_rooms likely rent for the day to keep your stuff ‘safe’, but what is the answer in StreetComplete? Quest exited.
If you know which
building tag you want to add, you can add it with the Android app Every Door instead. It has a buildings view and lets you type any tag you like. (Not like StreetComplete where you have to select it from a list.)
if you want to answer rarer building value not supported by SC then you need to leave note with photo and solve it later (or wait for someone else to tag it in iD/JOSM/etc.
Or switch to Vespucci or other editor and edit directly.