P5X-777 is a long-deserted planet with a large single moon and the remains of an ancient temple perched atop a high cliff in the middle of a forest wilderness. The temple was designed by the Furlings as a doorway to a utopian paradise on the planet's moon. The unfamiliar technology of the transportation device inside the temple does not use wormhole technology and is designed for limited distance. Inscriptions on the temple walls are in the language of the Furlings, including the lettering around the doorway lock which reads, "Only the righteous may pass."
Episode Reference: Paradise Lost