Suolong'ao is an ancient closed canyon in the hinterland of Ailao Mountain in Yunnan. It has vertical cliffs on three sides. The only entrance is a dangerous winding mountain road known as "Ghost Seeing Sorrow". The valley bottom is shrouded in miasma all year round and is isolated from the world. The villagers have inherited the custom of "ladder burial" from generation to generation. There is no tradition of burial and cremation. The deceased needs to be sealed with thirteen coffins and nailed to the "yin ladder" cut out of the cliff. The closer the coffin is to the bottom of the valley, the higher the seniority and the more dangerous it is.
