Yilong Zhu and Zhizhong Huang received intensive training by rock climbing professionals everyday for hours, since a month before and through the filming process. Yilong Zhu, being athletic himself (who plays basketball and holds a PADI diver certification), found rock climbing a new hobby after starring Cloudy Mountain (aka Feng Bao).
Yilong Zhu created the plot and related scenes of the "safety buckle" to enrich the character of Yizhou Hong, and drew a closure of the character's emotional trauma.
When filming a running scene at the slippery river bank covered with sharp gravels, Yilong Zhu fell down on the ground and injured his knee. He was not able to get up right away from the pain. However Yilong Zhu insisted on continuing despite on site medical staff advised him to take a break. He resumed shooting after some stretches and said "I feel fairly OK".
Part of filming took place in six unexploited caves that are pathless and not accessible by vehicle. The cast and crew walked 1-2 hours everyday to get to the movie site.
It took the crew five months to choose and finalize filming location in Guizhou. The tunnel and town were rebuilt from scratch. Machinery seen in the tunnel, such as trolley, rock drill, hydraulic trestle, are real life construction equipment. The derailed engine scene was filmed using a real life train.