Thanks to Katie Movelle (Queen Strange) for the following:
"Basque Mythology: Akelarre
[Akelarre literally means «field of the he-goat»]. The Akelarre is a plain of Zugarramurdi situated in front of the entrance to the cavern called Akelarren-leze «cave of Akelarre». It is believed that, in that spot and in that cavern, the witches of old met. In the vestibule of the cave, at a small height above the floor, a hole opens in the wall like a window, which, as the the neighbors of that locality say, is the hall where the devil, in the figure of a he-goat, received the witches. In the flat floor of the entry and of the vestibule, which preserve the remains of prehistoric homes, the devout of Aker -- or spirit in the form of the he-goat -- met to pay him their worship: adoration, offerings, telling of accounts, acceptance of orders."