The Maw

The Maw was an unstable and mostly unnavigable cluster of black holes located near the planet Kessel.
It was the site of Grand Moff Tarkin's Maw Station to build the first prototype Death Star. Tarkin knew that the Maw's near-inaccessibility and remoteness made it easy for him to hide the project.
The installation was actually located within a safe zone inside the cluster discovered just prior to the start of the project. The remaining area of the Maw was saturated in radiation, plasma, and strong gravitational forces. Anything that neared the edge of the Maw would notice pieces of their ships being pulled apart, and some brave smugglers and criminals used it as a shortcut past the Kessel Run.
The stability of the cluster itself was something of a mystery, with some believing that an advanced civilization might have constructed it, rather than it merging together like a normal cluster would.
The Maw was also the location of the creation and destruction of the Sun Crusher; it was constructed at the Maw Installation and destroyed when it was sent into one of the black holes within the Maw. Other superweapons designed and built there include the World Devastators, the Tarkin, the Ionic Ring, the Galaxy Gun, the second Death Star, and the Subspace Holotransceiver.
During the Yuuzhan Vong War, Lando Calrissian sponsored the construction of a space station called Shelter, which was built with the remains of Maw Installation as a refuge for fugitive Jedi Knights. Shelter was located at the very heart of the Maw and at one point housed the wartime generation of Jedi apprentices and surviving Praxeum students.
The Killiks claim to have placed the Maw Cluster around Kessel, but their collective memory makes this disputable; it is more likely that a member of the real makers joined one of their hives. Another candidate race is the Rakata.