Bi Fang retreated into the corridor, winding through the paths marked on the rock walls until he found a higher sloping terrain in the corridor.
After carving an arrow into the wall, Bi Fang explained to the drone.
"Within these caves, we must be careful of rising groundwater levels. Here, it's common to hear the water without seeing it. One step may be on solid rock and the next could unexpectedly be over a deep pool. In case of a cloudburst, it's quite possible for the water to fill the cave overnight."
"This scenario is extremely dangerous. In December 2009, seven cave explorers from France entered a cave at the border of France and Spain in the Pyrenees Mountains. When they reached 700 meters underground, the water level of the underground river suddenly rose, cutting off the exit route for three of them. The other four tried to rescue them without success before urgently seeking help from the outside world."