This episode explores whether ancient underground structures worldwide could provide evidence of extraterrestrial contact, focusing on three primary sites: the massive subterranean city of Derinkuyu in Turkey, discovered in 1963 when a homeowner broke through a cave wall during renovations; a cave in Ecuador rumored to contain metallic books inscribed with alien technology; and Dulce Base in New Mexico, where rumors persist of U.S. military collaboration with extraterrestrials inside a mesa. Ancient astronaut theorists, examining Derinkuyu's 13-story depth, ventilation systems serving 20,000 people, and engineering sophistication in the soft volcanic rock, suggest the city may be far older than conventional dating and required technological assistance beyond ancient human capabilities. They point to connections with Zoroastrian texts mentioning the creator god Ahura Mazda and interpret Native American legends of inner-Earth beings as potential evidence of a hidden extraterrestrial presence.
Mainstream archaeologists attribute Derinkuyu to the Phrygians around 800 BCE or possibly the earlier Hittites, built as a temporary refuge from surface invasions—a practical response to the region's history of conflict. The soft volcanic tuff stone, while requiring careful engineering to prevent collapse, was workable with bronze-age tools, and the absence of catastrophic cave-ins demonstrates ancient builders' material knowledge rather than alien intervention. For skeptics, the episode offers a fascinating look at genuinely impressive ancient engineering achievements and raises legitimate questions about how pre-industrial societies accomplished such ambitious projects, even if the answers lie in human ingenuity rather than extraterrestrial contact.
Archuleta Mesa / Dulce Underground Base
United States · Modern
UFO researchers and conspiracy theorists claim that the Archuleta Mesa near Dulce, New Mexico hides a secret underground base where the U.S. military collaborates with extraterrestrial beings, supported by local Apache eyewitness accounts of UFOs and strange noises from vents in the mesa. No verified evidence of such a base has been established, and the claims remain unconfirmed.
Cave of Tayos
Ecuador · Pre-Columbian
Ancient astronaut theorists, inspired by Erich von Däniken and explorer Stanley Hall, claim the Cave of Tayos contains a vast 'metal library' of books inscribed with advanced or alien knowledge, as well as large artificial-looking doorways that geologists could not easily explain. The 1976 Hall expedition found a tomb chamber with items dating to 1500 BC but no treasure, and mainstream scholars treat the cave as a natural Ecuadorian cave system with localized indigenous significance.
Cuenca (Father Crespi Collection)
Ecuador · Pre-Columbian
Ancient astronaut theorists argue that the elaborate metallic artifacts given to Father Carlo Crespi by Shuar people in Cuenca display symbols and craftsmanship from an unknown advanced or extraterrestrial culture, with some tablets bearing unreadable writing possibly linked to the metal library of Tayos. Mainstream archaeology has not authenticated the artifacts' origins, and much of Crespi's collection disappeared before his death in 1982.
Derinkuyu Underground City
Turkey · Phrygian / Byzantine
13 stories deep, extending 280+ feet underground
Ecuadorian Cave Complex
Ecuador · Amazonian Indigenous
Ancient Aliens suggests a cave in Ecuador may contain metallic books inscribed with secrets of alien technology, implying evidence of extraterrestrial knowledge transfer to ancient civilizations.
Goreme / Cappadocia
Turkey · Byzantine
Entire underground civilization carved from soft volcanic rock
Mayan Underground Temple near Tahtzibichen (Xibalba caves)
Mexico · Maya
Ancient astronaut theorists contend that the physical features of this cave system—rooms matching descriptions of torture chambers, bat rooms, cold rooms, and a river of blood from the Popol Vuh—suggest Xibalba was real, and that its 'lords of the dead' may have been extraterrestrial beings. Archaeologist Guillermo de Anda argues the cave predates the Popol Vuh and is the actual Xibalba of central Yucatán, though mainstream archaeology views it as a site the Maya modeled or interpreted through their existing mythology.
New Mexico Underground Military Base
United States · Modern
Ancient Aliens reports rumors of the U.S. military working alongside aliens in a secret base inside a mesa in New Mexico, suggesting ongoing extraterrestrial collaboration.
Yucatan Cave System
Mexico · Maya
Ancient Aliens claims recent archaeological discoveries in the Yucatan may point to an extraterrestrial reality behind underground alien activity and ancient visitations.