The Hrakert Rift was a deep valley under the oceans of Manaan. It was the source of the kolto that the planet was famous for manufacturing, and home of many firaxan sharks, including a massive firaxan believed to be the Progneitor.
The Republic built a secret facilty on the edge of the rift to harvest the kolto at the source, but the station was later destroyed after it woke the Progneitor.