Hyakumanjou Labyrinth

What if real life could "glitch"?Reika and Yoko, two students, wander in a huge building, a real never-ending labyrinth defying imagination. Their only clue: a mysterious message on a low table, signed by Tagami, a famous video game creator, who seems to know more about this place.What is the real nature of this place ? Why are Reika and Yoko humanity's only hope?