In the distant past, when the Jedi Order was first venturing into the galaxy, the order sought to establish a new home and training grounds on the planet Ilum. These ancient Jedi built a new Jedi Temple above Ilum's network of crystal caverns, and while the planet's climate was far from idyllic, its isolation and supply of lightsaber crystals made it an ideal place for schooling Padawans.
Careful to protect Ilum against the darkness that had threatened them on Tython, the ancient Jedi kept the hyperspace routes to Ilum secret from the rest of the Republic. The preferred means of learning the route required Force sensitivity and became the first trial of many an aspiring Jedi. But warfare with the Sith under the fallen Jedi Exar Kun led to the destruction of the training grounds, and in the centuries since, Ilum has been home to only a select few.
The temple became a place for young Jedi to travel and build their lightsabers, and where they might meditate in silence. It was a place of beauty and tranquility and crystalline perfection. Until today.