The Myhr'an internment camp was an enclosed Myhr'an prison facility within a larger starbase on Rhinessa VI.
In 2372, Federation civilians and Starfleet personnel were being held there. The USS Cantabrian, working on evidence of this, went to Rhinessa VI and freed as many prisoners as they could.
The Cantabrian, with help from the USS Aotearoa, destroyed the camp and escaped. (Star Trek: The Cantabrian Expeditions: "Two Hit, One Stone")