The Atrium—a colossal, shifting, neoclassical labyrinth that looks like a cross between a luxury grand estate, an infinite museum, and a subterranean bunker. ​You are a "Delver," an explorer who stumbled into this pocket dimension through a glitching elevator in the real world. The only way out is forward. There are 100 structural checkpoints (Thresholds) you must cross to find the exit, but the architecture distorts itself the deeper you go.