Elis

The sacred enclosure of Haides and its temple are opened once every year, but not even on this occasion is anybody permitted to enter except the priest. The following it the reason why the Eleans worship Haides; they are the only men we know of so to do. It is said that, when Herakles was leading an expedition against Pylos in Elis, Athena was one of his allies. Now among those who came to fight on the side of the Pylians was Hades, who was the foe of Herakles but worshipped at Pylos. Homeros is quoted in support of the story, who says in the Iliad: And among them huge Haides suffered a wound from a swift arrow, when the same man, the son of aigis-bearing Zeus, hit him in Pylos among the dead, and gave him over to pains.

If in the expedition of Agamemnon and Menelaus against Troy Poseidon was according to Homer an ally of the Greeks, it cannot be unnatural for the same poet to hold that Haides helped the Pylians. At any rate it was in the belief that the god was their friend but the enemy of Herakles that the Eleans made the sanctuary for him. The reason why they are wont to open it only once each year is, I suppose, because men too go down only once to Haides.

(Pausanias, Description of Greece 6.25.2)