Ananke Alpha is a spherical, maximum security, top secret Federation prison complex. It was constructed in the 2320s as a facility to hold extremely dangerous criminals and those who were difficult to detain. The complex was located in an extremely remote star system with no planets.
Shortly after the end of the war, a small group of Cardassian commandos, part of the Rom Knights, broke in to the facility with the intent of assassinating the Female Changeling, but their mission was a failure. (ST comic: "Alien Spotlight: Cardassians")