View looking southeast at the excavations of the "New Plutonium." Note the doorway on the lower left, and the reflections on the water partially visible in the center of the image. There are apparently five long stairs to the left of the water. Evidently, people could watch rites associated with the Plutonium from these stairs.
Previously it was thought that THIS was the entrance to the Plutonium.
In March 2013, Francesco D'Andria, professor of classic archaeology at the University of Salento and excavator at Hierapolis announced that he had excavated the well–known, to ancient authors, Plutonium at Hierapolis—known as the gate to the Underworld.
The following reconstructed image is from a very useful article in "seeker.com" that describes the discovery in detail. The view of this image is the opposite of that of my image above.