The Imperial outpost on Kejim.
The Imperial listening post was defunct after the destruction of the Death Star however in the time of the Empire Reborn, it started operating again, using older Imperial codes. The signals, although weak, were intercepted by the communications team of the New Republic Intelligence and attempted to decrypt it.
This prompted Mon Mothma to send mercenaries Jan Ors and Kyle Katarn to the world to investigate.
A partially successful decryption of these messages revealed that they seemed to be intended for Imperial Remnant Admiral Galak Fyyar, and they mentioned the Valley of the Jedi and "Reborn." Katarn was reluctant to revisit a sensitive subject from his past, so Mon Mothma offered him double his usual fee. Ors quickly accepted this on the pair's behalf, and this set into motion a chain of events which would change Katarn's life and eventually eliminate a major threat to the Jedi and the security of the New Republic.
Upon exploring the Imperial outpost, Katarn found that the site had indeed been reoccupied. Probing further into the base, he discovered a laboratory where strange medical experiments were performed using high-energy equipment and unidentified crystals.
It was later discovered that Admiral Fyyar, in association with the Dark Jedi Desann, was using the laboratory for experiments in infusing Force abilities into subjects with little or no innate Force-sensitivity via Artusian crystals as part of Hethrir's Empire Reborn movement. Kyle Katarn eventually shut down the Kejim laboratory by setting off a bomb.