The initiated then entered the cave dressed in black woollen garments, and remained within for thrice nine days. Everything points to the existence of conceptions similar to those that we found expressed in the cult of Zeus Trophonios at Lebadeia.
Rohde argues that the Idaean cave-cult of Zeus constitutes a chthonic mystery religion of initiatory descent and divine encounter structurally parallel to the oracle of Trophonios.
, Psyche: The Cult of Souls and the Belief in Immortality among the Greeks, 1894thesis