[exDemMom]

Hmm.

I always imagined domes on the lunar surface, open to the starlight, where people could live and always look up to view the celestial scenery. In a cavern, they would be stuck looking at rock. Maybe shielded windows could give them a view.

[SunkenCiv]

Probably both.

“They could be entrances to a geologic wonderland,” says Mark Robinson of Arizona State University, principal investigator for the LRO camera. “We believe the giant holes are skylights that formed when the ceilings of underground lava tubes collapsed.”
http://science.nasa.gov/science-news/science-at-nasa/2010/12jul_rabbithole/

http://www.universetoday.com/119634/there-could-be-lava-tubes-on-the-moon-large-enough-for-whole-cities/

http://news.discovery.com/space/lunar-lava-tubes-could-host-underground-moon-cities-150402.htm