Glastonbury Tor

Glastonbury Tor is a hill overlooking the town of Glastonbury, England. The Ancients, including Myrddin (Merlin) hollowed out the hill and created a vault known as Avalon, where he used technology to hide Avalon from any scientific studies. During Earth's medieval period, people believed that the hill was hollow and contained an underworld known as Avalon. The "myth" turned out to be "disproved" after several scientific studies. However, SG-1 managed to find Avalon underground, using the Asgard sensors to scan the Tor.