Despite NASA denials, all the Structures on the Moon are not natural, nor are they man-made. The Moon, so close to Earth yet clear of the Earth's congested surface and atmosphere, has been used by many alien groups, and for many reasons. Currently it is a home for those in the Service-to-Self, who reside there in 3rd Density. However, their home is not what has humans talking, as they are placed on what is called the dark side of the Moon, never visible from Earth. During the era when the hominoid visitors from the 12th Planet were running mining operations on the Earth, primarily for gold, they used the Moon as a communication outpost, as it was free of cloud cover and allowed for a more precise aim through space. The Moon was thus a booster, magnifying signals sent from Earth and sending a clear strong signal into space. These communications went to their mining operations on Mars, but primarily to their home planet when it drew near, as the opportunity for contact with home was not to be missed.
However, earlier still the Moon was used as an outpost by groups conducting genetic engineering operations on Earth, as many of these groups found the Earth to be a virtual swamp of life - murky, unpredictable, crawling with bugs and germs, and subject to erratic weather extremes. Their scientists had their specimens brought to the lab for detail work, and returned the fertilized ova for implantation. To these aliens, the shuttle to Earth was insignificant, where the controlled environment of their Moon cities was a relief. Thus, the structures seen on the Moon are ancient, and are a combination of the shards of Moon cities from genetic engineering operations and the shards of communication crystals - abandoned and idle but causing quite a stir among humans these days.