The Cuatrian would lie on his back and picture an Opening to a Dark place. Each person’s entrance was different; Chiara herself envisioned a cave, but the imagining could be a temple, a closet, a ‘fairy house,’ or a fountain. As long as the opening leads below the surface of the world, it is acceptable.

Next, the seeker would listen closely until he began to hear a faint ringing noise: the “Voice of the Swallows,” who are sacred to Antuor. Eventually the would will become a two-syllable ‘word,’ similar to a Hindoo “mantra.” The Cuatrian would then begin repeating this word, internally, as though a chant.

As the word was repeated, the visionary would slowly be drawn into the darkness of the Hypogeum and a series of colors would begin to appear. This word and series of colors became the ‘key’ to the Hypogeum, through which he could access this state at any time. This key would only work for the individual Cuatrian.

Source: Entering the “Hypogeum”: A Method – Quatrian Folkways – Medium