Following the studies carried out on site in 1998, a geologist of the Italian National Research Council, Luigi Piccardi, recognized that the origin of both the Ploutonion and of the nearby Apollo's Oracle of Hierapolis was linked to the existence of the surface trace of a seismic fault, on which both sanctuaries were purposely built and which was revered as Gateway of Hades.

[6] Though the exact age of the site is currently unknown, the nearby city of Hierapolis was founded around the year 190 BC by the King of Pergamum, Eumenes II.

It is a small cave, just large enough for one person to enter through a fenced entrance, beyond which stairs go down, and from which emerges suffocating carbon dioxide gas caused by underground geologic activity.

Behind the 3 square metres (32 sq ft) roofed chamber is a deep cleft in the rock, through which fast-flowing hot water passes, releasing a sharp-smelling gas.

[citation needed] During the early years of the town, the castrated priests of Cybele known as the Galli descended into the Ploutonion, crawled over the floor to pockets of oxygen or held their breath.