Special crystal formation in an underwater palace
See also: Piraus Crystal
Located on the planet of Piraus-3, the Aquatic Geode of Piraus is a crystal formation under the sea which grows special crystals that are particularly attuned with the Force.
The Aquatic Geode is hidden under an underwater palace which used to be be guarded by an order known as the Leviathans, the guardians of palace and temples constructed around the formation. As their numbers dwindled and the site was abandoned, an order of Maesters took over, and recently the Jedi took over their duty in turn.
The Aquatic Geode is now guarded by the Jedi, who following the tradition of the Maesters sometimes use a crystal from the formation in their lightsabers.