These caves are natural, though metal walkways have been placed down to move about on. With the Knights guiding you, you follow these walkways into some sort of room. The walls and floor and ceiling are all made from a dark metal.
There is an altar on the far end, with two cloaked figures standing before it. One is taller than the other.
"We've brought him," Crutch says from somewhere behind you. He steps past. "He was armed only with this." He produces your lightsaber and holds it out to the taller figure.
"Excellent," he says, turning to face you. It is Lothar.