Introduction to the back room of the underground palace: The back room of the underground palace is the coffin room. There is a corridor connecting the two rooms. Except for the door, which is made of stone, the rest is made of bricks and the roof is paved with square bricks. The four walls and top are covered with white ash, and the walls are decorated with double ink lines. The two doors are of the same shape, and the door knocker is locked with a 57 cm long spring-type iron lock. The back room is 5.45 meters long from north to south and 8.2 meters wide from east to west, making it taller and more spacious than the front room.