Location from Attack on Titan by Hajime Isayama
An underground cavern beneath a chapel where the Founding Titan was passed down through the Reiss bloodline for generations. Where Historia refused to eat Eren and chose to be her own person.
Beneath an unremarkable chapel in Wall Sina territory lies a cavern of crystallized walls and terrible purpose. For generations, the Reiss family — the true royal bloodline — performed a ritual here: the current holder of the Founding Titan would be consumed by their successor, passing down not just the power but the will of the First King, who believed Eldians deserved to die for their sins. The cavern is beautiful in the way that cathedrals built for human sacrifice are beautiful — vast, luminous with crystal formations, designed to inspire awe in the person being asked to eat their parent. Rod Reiss brought Historia here to consume Eren and reclaim the Founding Titan. Instead, Historia chose to shatter the syringe, reject her father's legacy, and burn the chapel down. The cavern still exists beneath the ruins. The crystals still glow. Some prisons are harder to destroy than their walls.
Also known as: the Reiss cavern, the chapel, the crystal cavern