P7X-377 is a planet in the Milky Way galaxy that is home to the Omeyocans. The planet has an enormous pyramid well over one thousand meters high, which houses a crystal skull and at least one "giant alien," Quetzalcoatl. This pyramid is filled with beautiful stalagmites and a fatal level of lepton radiation, believed to be the source of power for the crystal skull to transport people from one skull to another clear across the galaxy.
Nicholas Ballard is believed to be the first human to visit P7X-377 via a crystal skull found in the ruins of Belize, which teleported him into the enormous pyramid to encounter the giant aliens. When he did not respond to their words of friendship, they sent him back to the ruins. He tried for years to return to 377, but without the lepton radiation from the destroyed chamber in his expedition, he was unable to duplicate the experience. (SG1: "Crystal Skull")