"[Caves] make available the main structural parts of a possible human base without requiring complex construction activities,” one researcher noted Kimberlee Speakman is a digital writer at PEOPLE.

On July 20, 1969, Apollo 11 astronaut Neil Armstrong announced his historic arrival on the ancient lava plain of Mare Tranquillitatis with the following message to NASA: "Houston, Tranquility Base ...

In this photo provided by NASA, astronaut Edwin "Buzz" Aldrin poses for a photograph beside the U.S. flag deployed on the moon during the Apollo 11 mission on July 20, 1969. (Neil Armstrong/NASA via ...