Here is the crater Messier "A" from the Moon, within the Mare Fecunditatus. Its dimensions are 13 X 11 kilometers. This was a drawing from one of the members of the British Astronomical Association. I shamelessly lifted it from the David Hatcher Childress video, Extraterrestrial Archaeology. You can see that there is some railway within, or perhaps some kind of terraced stairway, which descends. So the Moon seems to have tunneling and, by extension, cavern worlds, within.
I like the David Hatcher Childress material. Whatever happened to him?