The moon is the closest neighbor of the Earth, and now mankind continues to actively study our satellite. Not so long ago, the Chinese sent a station to the moon, which completed a number of scientific tasks. Now the European Space Agency plans to join the direct study of the moon. Only not its surface, about which a lot is known, but caves.
Yes, there are caves on the moon, and quite a few. Some of them can serve as a reliable shelter for lunar colonists, which will allow them to avoid a number of dangers that threaten on the surface. ESA collected lots of ideas proposed by scientists and engineers and selected the five most promising. Then another stage of selection followed, so now the agency has three ideas that are planned to be implemented. They are all interconnected.