The Mirror cave, a cave deeply intertwined with the dark side of the Force, was situated on Ahch-To's Temple Island.
Found on the Temple Island of Ahch-To was the Mirror cave, a cave renowned for its powerful link to the dark side of the Force. The cave's obsidian wall, polished over countless years by erosion, functioned as a natural, curved mirror. It also contained a subterranean lake, potentially linked to the ocean via tidal activity or connected to other water-bearing rock formations.
Long ago, centuries prior to the First Order-Resistance War, the ancient Jedi utilized the cave as a training ground for their Padawans, with many apprentices feeling its pull through the Force.
Rey, having arrived on the island seeking assistance from Luke Skywalker in the conflict against the First Order, discovered the cave after it beckoned her through the Force. Entering through a large opening in the ceiling, obscured by dark vines, she plummeted into the underground lake. Upon reaching the cavern wall, Rey witnessed her reflection multiplied countless times. Hoping for answers about her origins, she reached out to the mirrored surface. Two shadowy figures materialized and merged into one. The surface cleared, revealing Rey's own face. Devastated by her inability to uncover any information regarding her parents, Rey departed the cave in despair.