Cathedral Ship is a massive type of Gnosis roughly ten thousand kilometers in diameter. If it were a perfect sphere, it would have a surface area of about 314,000,000 kilometers.
In Episode I, the Elsa became lost inside a Cathedral Ship that was the transformed planet Ariadne, which vanished during a Link Experiment with a Zohar Emulator. Remnants of the planet are also found inside the Cathedral Ship when exploring it. Gnosis are attracted to the Zohar as well as to its emulators, so, when the Woglinde attempted to leave with the Zohar Emulator, the Cathedral Ship sent legions of Gnosis to collect it. The Zohar Emulator remained inside of the Cathedral Ship until Shion and friends were drawn into its core. Commander Cherenkov, sent to retrieve the Emulator for Margulis, was turned into a Gnosis right in front of the protagonists, just before its disappearance. The Zohar Emulator then fell into the hands of the Kukai Foundation.