Grennokar

Grennokar was an Obsidian Order base and detention center located on Harkoum. The base was hidden from a view by a holographic cloak.

Among those held there were criminals, dissidents and aliens. Some prisoners were executed, although others were used for hard labor. There were also Cardassian scientists based there who subjected prisoners to biogenic weapons, new surgical techniques and as test subjects for refining torture techniques. 

Soon after Cardassia joined the Dominion, Obsidian Order scientists such as Drune Omek and Strell Vekeer began experimenting on Jem'Hadar. It is believed their goal was to discover the code with which the Founders had genetically engineered into them the Jem'Hadar's loyalty to the Changelings. 

Grennokar was abandoned after the Dominion War. It soon became Iliana Ghemor's base of operations. 

In 2377, Taran'atar was summoned to Grennokar by Intendant $𝜇$. Elias Vaughn and the crew of the USS Defiant (NX-74205) (II) followed the Jem'Hadar, but were unable to stop him before he transported to the mirror universe and the facilities self destruct was activated. However, Vaughan discovered the tests on the Jem'Hadar and he and his daughter Pryn Tenmei were able to escape Grennokar on top of the piloted by the mirror universe $𝜇$ before the facility was totally destroyed.