Somewhere deep in the cosmic wilderness of the Unknown Regions, Ilum is a lonely world virtually unknown to all but the mystics of the Force. Drawn by the sheer magnetism of its vergence, hyperspace scouts of the Jedi Order first discovered it in 22,800 BCGT and Ilum's coordinates have remained a closely guarded secret ever since. Recognized as a sacred place, those who can sense the planet and navigate the turbulent hyperspace currents to reach it simply don't discuss it with those who cannot.

Said to emit one of the brightest Force auras in the galaxy, Ilum's lithosphere is honeycombed with a vast network of volcanic tunnels where Adegan crystals, a key component in lightsaber construction, have formed in very great abundance. The entire labyrinth of caverns and shafts has never been completely explored, although the Jedi built a majestic temple over the largest entrance and surveyed most of the surrounding complex. These caverns would become decorated with elaborate sculptures depicting the history of the Ashla orthodoxy, carved directly into the planet's vantablack stone.

For thousands of years, the Jedi Order maintained the security of the Crystal Caves, one of the most important destinations in a young student's journey. A training center grew up around the temple to accommodate the flow of pilgrims arriving to participate in the ceremony of the Gathering and face its profound challenges. There is nothing routine about navigating the Crystal Caves; the sheer power of the concentrated Force energy is said to cause intense visions, and indeed, some mystics have descended into the labyrinth and never returned.