On this video, at time stamp 8:52, the narrator Chris suggests that The Moon has been inhabited, could still be inhabited, and that it might be inhabited by an underground population.
People, this is a conclusion that Chris has arrived at by himself, because we haven't had contact with him, and I haven't seen him on the Facebook hollow earth lists, either. On that video, he didn't specifically come up with any evidence of under-the-surface worlds. However, on some other videos, he has.
I think that it would be interesting to establish contact with him because he is extremely talented, curious, intelligent and well-informed. I'll look into it.
In the meantime, go to Lunar anomalies and beyond, and click on a few of his videos, and don't forget the thumbs up. He needs a few and deserves them.