Pluto's Gate
By AlMare - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=1773283
Pluto was the ruler of the underworld in Greek mythology. He was known as Hades, but as time progressed, Hades became more used as the name of the underworld than the god. He represented the positive aspects of the underworld, as well, as well as being conflated with Plutus, the god of wealth, because of the chthonic origin of mineral wealth. He was revered as a stern ruler and loving husband to Persephone, with whom he was monogamous. He was also sometimes called Zeus of the Earth or Zeus Chthonios, and was important to agriculture. Sanctuaries dedicated to Pluto were known as ploutonion and visitors would seek healing and prophetic dreams. These were also connected with Persephone, Cybele, and Apollo.
By Carole Raddato from FRANKFURT, Germany - The Plutonium (Pluto's Gate), a sacred cave believed to be an entrance to the underworld and the oldest local sanctuary, Hierapolis, Phrygia, Turkey, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=55185949
One of these ploutonion was known as Pluto's Gate or the Gateway of Hades. Located in Hierapolis, which is near Pamukkale, Denizli Province, Turkey. It is located near the Oracle of Hierapolis, dedicated to Apollo, which is tied to to a fault line through the area. The age of the shrine is unknown, but the city of Hierapolis was founded in 190 BCE. Pluto's Gate is located in a small cave, large enough for only one person to enter at a time, though entering could be suffocating. Before the cave, an enclosure of 2,000 square meters was blocked off to keep priests and visitors safe from the gases while they could purchase animals to check if the cave was safe to enter. Early in its history, a castrated priest of Cybele, the Galli, would climb through the cave, holding their breath between pockets of oxygen to prove they were immune.
Source: https://www.express.co.uk/news/world/2005622/gate-hell-used-god-death
The plutonion was in use until the 4th century CE, and sporadically until the 6th century CE when an earthquake destroyed the site. Because of its location on a fault line, the area around the cave can have carbon dioxide levels as high as 80%, making it incredibly deadly to a person, because this fault line runs near a volcano and that volcano vents through the cave.
