According to Discovery News, hell's gate has been discovered in Turkey by an archeological team led by Francesco D'Andria — Professor of Classic Archeology at the University of Salento. D'Andria announced his discovery in March at a conference on Italian Archaeology in Istanbul.
Also known as Pluto's Gate, the rediscovered cave was celebrated as the portal to the underworld in Greco-Roman mythology and tradition where it was described as filled with "lethal mephitic vapors." Ancient priests recorded that they threw birds into the cave to test the strength of the vapors and they died immediately.
The archeologists that discovered the site found it covered by an array of abandoned and broken ruins. After initial excavations, they found inscriptions with dedications to deities of the underworld carved into the stone, and — like the ancient priests had discovered — birds, trying to get close to the warmer air rising from the cave died immediately.
Apparently, the site was functional until the 4th century AD and was visited regularly by pilgrims looking to receive visions and prophecies from the gods of the underworld (basically hallucinations from the noxious fumes rising from the ground). Christians destroyed what was left of the deserted site in the 6th century AD, and until D'Andria's recent discovery, this "gate to hell" has existed only in the history books.