Katratzi is a legendary, moon-sized orbital base belonging to the Scarran Empire, said to be the emperor's seat of power and heavily fortified. It was only spoken of in hushed rumors and those outside of the Scarran Empire were unsure if it existed at all until the crew of Moya found evidence of it.
The base itself could only be reached by traveling through a gateway station into Scarran space. After this, it was still difficult to detect as it orbited the planet Trelast in a mirror of Trelast's natural moon. Once inside the base, unless one had been invited or was part of the hierarchy of the Scarran Empire, leaving alive is highly unlikely.
Eventually, however, Katratzi was destroyed by the crew of Moya.
Katratzi appeared in the fourth season of Farscape.