Sinity's Fist was a secret hangar, located deep within Armageddon Palace, near the very core of the planet (Naomi). Though there were many other hangars located about the Palace, Sinity's Fist was the largest; it was a monstrous space, filled with ships of all types to service Sinity and his apprentices, who were some of the very select few who knew of its location. Sinity's flagship, Medusa, was docked in Sinity's Fist when it was not in use. The large hangar was also home to Darth Execta's flagship, Guillotine, as well as Darth Monsant's flagship, Dominance.
Because the hangar was located close to the center of the planet, direct access to space was limited. Therefore, a tunnel led from Sinity's Fist to the outside of the planet through the Great Sea, carved into the ice. The kilometer-wide tunnel ended shortly before the surface; in order to maintain secrecy, a 5-metre wide sheet of ice remained over the tunnel's entrance -- Sinity knew that a few proton torpedoes could easily blast through the ice, opening up the way for any cruisers passing through.
Sinity kept a special group of 200 or so slaves working in the hangar. He heightened their amount of mind-control, so that they had absolutely no free-will of their own whatsoever. He also prevented them from speeking by damaging their mouths, in order to keep the hangar an absolute secret. These slaves also lived apart from the others, in secret caves close to Sinity's Fist.
At any given time, numerous Haphaestus-class Star Destroyers, Cerberus-class Star Destroyers, and Athens-class Star Cruisers could be found docked in Sinity's Fist. Many important ships, such as Sinity's Rage, Pandora, and Hades docked in Sinity's Fist when at Armageddon Palace.
Because Sinity's Fist was located deep within Naomi, it was essentially safe from the Naomic Cleansing. At the time of Sinity's death, Medusa was stationed inside the secret hangar. Because the hangar was never found, it could be said that if anyone ever discovered Sinity's Fist, they could easily get their hands on one of the largest and deadliest ships ever built.