Historians located the site in the ancient Phrygian city of Hierapolis, now Pamukkale, describing the opening as filled with lethal mephitic vapours, the 'Discovery News' reported.
"This space is full of a vapour so misty and dense that one can scarcely see the ground. Any animal that passes inside meets instant death," Greek geographer Strabo, who lived between 64/63 BC -about 24 AD, wrote.
"I threw in sparrows and they immediately breathed their last and fell," he added.
The finding was made by a team led by Francesco D'Andria, professor of classic archaeology at the University of Salento, who conducted extensive archaeological research at the World Heritage Site of Hierapolis.
"We found the Plutonium by reconstructing the route of a thermal spring. Indeed, Pamukkale' springs, which produce the famous white travertine terraces originate from this cave," D'Andria said.
"People could watch the sacred rites from these steps, but they could not get to the area near the opening. Only the priests could stand in front of the portal," D'Andria said.
Small birds were given to pilgrims to test the deadly effects of the cave, while hallucinated priests sacrificed bulls to Pluto, he said.
The ceremony included leading the animals into the cave, and dragging them out dead.
"We could see the cave's lethal properties during the excavation. Several birds died as they tried to get close to the warm opening, instantly killed by the carbon dioxide fumes," D'Andria said.
Only the eunuchs of Cybele, an ancient fertility goddess, were able to enter the hell gate without any apparent damage, the report said.
"They hold their breath as much as they can," Strabo wrote, adding that their immunity could have been due to their "menomation", "divine providence" or "certain physical powers that are antidotes against the vapour".
D'Andria said the site was fully functional until 4th century AD, and occasionally visited during the following two centuries.