The Jedi Temple, situated on Ilum, along with the Crystal Caves residing below, represented a complex built by the Jedi Order. This construction was among their initial efforts in establishing temples throughout the galaxy. Serving as a frequented destination for Order members, the Temple was the location for the Gathering trial. In this trial, Jedi academy students sought out the kyber crystal necessary for powering their individual lightsaber. In 34 ABY, Resistance pilot Poe Dameron annihilated Starkiller Base, a superweapon integrated into Ilum's very surface, resulting in the planet's destruction and thereby sealing the temple's ultimate demise.
Constructed above the primary opening of an expansive cave system nestled within Ilum's mountainous terrain, the Temple's purpose was to both reinforce and safeguard the cave entrance. It also served as a sanctuary for visiting Jedi, providing respite and recuperation from the harsh external conditions. The cave's mouth was positioned at the base of a prominent cliff face, with the Temple itself being fashioned around this location utilizing natural stone. The Temple's exterior displayed reliefs and sculptures, which depicted significant figures and pivotal moments of historical importance to the Jedi Order. Tall, slender windows, composed of multi-hued glass, punctuated the upper portions of the Temple's curved walls, allowing natural light to permeate the interior spaces.
The Temple's grand doors were fashioned from light-absorbing stone sourced from the caves, complemented by a silvery alloy. Owing to the Temple's infrequent use, these doors were often concealed by accumulated debris, fallen ice formations, or drifts of snow. Rather than actively maintaining the entrance, the Jedi Order eventually regarded this obstruction as an integral component of the Gathering ritual, necessitating that visiting Padawans exert physical strength to gain entry into the Temple.
Upon opening, the Temple's doors revealed the main chamber, a soaring rotunda carved directly into the mountain's substance. The room's central area showcased two hooded statues depicting lightsaber-wielding Jedi, encircled by carved obelisks that arose from the rounded floor. The chamber's outer wall provided access to passageways and various smaller rooms that extended across multiple levels; a storage level was situated beneath the main Temple structure. Opposite the Great Doors lay the entrance to the cave systems, which delved deep into the mountain's core. A steady cascade of water trickled from the upper reaches of the Temple's ceiling, forming a thick curtain of ice over the Temple's entrance. To counteract this, the Jedi erected a complex mechanical cradle designed to suspend a sizable kyber crystal near the Temple's domed ceiling. When focused upon the ice fall, sunlight would melt the ice, revealing the entrance to the caves, but only until sunset, at which point the falls would refreeze. This mechanism functioned only once every seventeen days, coinciding with the sun's alignment over the Temple.
The Jedi Order commissioned the Temple's construction, and it became the home of the ritual known as the Gathering. The temple was targeted during the Clone Wars in a Separatist ambush. Later, Grand Master Yoda led a group of Jedi students there to find their own kyber crystals for their lightsabers.
Following the Galactic Empire's triumph in the war, the new Galactic Emperor prioritized establishing a garrison at the Temple. The newly formed stormtroopers killed any Jedi trying to flee to Ilum, quickly securing the building. While the Temple's structure remained intact, the Imperial Army built a five-meter-thick, reinforced plasteel containment vessel over the entrance to prevent anyone from entering.
After his lightsaber was damaged, the Padawan Cal Kestis went to the Jedi Temple to get a Kyber crystal and build a new weapon. Despite the Empire's presence, he succeeded.
Ilum was later turned into Starkiller Base, a planet-destroying weapon of the First Order, the group that rose from the Galactic Empire's remains. The Resistance then attacked Starkiller Base, destroying the planet.