The Geysers where they live.
Palikoi (palikos, singular) are geyser spirits/gods and oversee sacred oaths.
History[]
According to The Hidden Oracle, the palikoi are twin sons of Zeus and Thaleia, one of the Charites. In Percy Jackson's Greek Gods, however, they are the children of Hephaestus and the mountain nymph Etna. In a version of the myth, Thaleia is a nymph, daughter of Etna and Hephaestus, and she's the mother of the Palikoi with Zeus.
There are currently two palikoi in the forest at Camp Half-Blood called Pete and Paulie. After Meg McCaffrey is taken by the Myrmekes, Pete gives Apollo directions to their nest. Paulie was imprisoned by Nero at the gates of the Grove of Dodona. He was later freed by Meg and Apollo when they saved the grove.