Days after the barrier fell, a tower appeared overnight on a plateau southeast of Khorinis. No construction, no workers, no warning. The locals noticed and kept their distance. That was the right instinct.
Xardas was the supreme magician of the Circle of Fire before he turned his back on Innos and everything that came with the title. What Beliar offered him instead was apparently worth it. The tower reflects that trade. Pentagram on the floor, altar to a dark god upstairs, demons left to guard the place when the owner is away. Not a building people visit voluntarily.
The hero wakes up inside it at the start of the story.