You been hearing those reports from the Deep Prison?"
"Don't remind me. Sounds like a war zone down there."
"The convicts and Imps I expected, but the things they're finding down there…Two Republic soldiers
The Tomb, also known as the Deep Prison, was a massive prison complex created by the Infinite Empire on Belsavis. It was later converted into a part of the wider Belsavis prison by the Galactic Republic.
History
It was discovered by the Galactic Republic fifty years before the Great Galactic War and converted into a Republic prison by the Strategic Information Service. During the Great War it was used to house Mandalorians, Sith Lords, and Sithspawn. During that war, the Sith Empire sent strike teams to the planet in an attempt to free its members from their imprisonment.
At one point, Executor Krannus intended to overload the Rakatan power core located in the lower levels which would have created a hyperspace ripple that would have destroyed the entire star system.