Zhenkunwei

There is such an ancient building in the world. It is isolated from the world. People inside can't get out and people from outside can't get in. There are five layers in total, which are closed in a ring shape. It covers a large area and can accommodate ten thousand people. The building has everything needed for human life. The name of this building is: Zhenkunwei. People in the building need to remember that the fifth floor must not be entered!