The Extinction Site Administration had hundreds of espers employed. In order to keep these espers in shape, there was a huge and advanced training facility.
The training center had a large gym, and the equipment were all tailored to the strengths and capabilities of espers. Other than that, there were also single training rooms where espers were allowed to shut themselves away to train in peace.
Han wanted to try his Void End, so he booked a large single training room. At this moment, the majority of espers were exploring the Extinction Domain so there weren't a lot of people there. Han went to the single training room on the top floor. It was about 200 square meters with large glass windows that extended to the ground. The floor and the wall were all built from enhanced carbon fiber. The structure was even stronger than steel, but also lighter and more resilient.