Here is something to consider;

Most private garages in West Germany have a grease pit in the floor, where a person would stand to service the vehicle from underneath, even in areas where zoning prohibits owners from washing and servicing vehicles at their residence.

My landlord in those days did his best to explain gamma radiation and slit trench protection, but back in the cold war days, we GIs thought we were cannon fodder anyway, so I didn't pay a lot of attention.

A grease pit would be handy to service a vehicle from, provide protective cover, make a room within a room, secure storage, serve as a changing room, latrine, operating room, or morgue.

Shucks, I talked myself into it. I'll go rent a concrete saw tomorrow, fire up the backhoe, and start building forms for steps and walls.