Many tunnels have standing pools of water which could conceal holes in the floor. Pools of water also are common at the bottom of shafts. It is usually impossible to estimate the depth of the water, and a false step could lead to drowning. Ladder rungs are missing or broken. Some will fail under the weight of a child because of dry rot.
Vertical ladders are particularly dangerous.
Areas that are likely to cave often are hard to detect. Minor disturbances, such as vibrations caused by walking or speaking, may cause a cave-in. If a person is caught, he can be crushed to death. A less cheerful possibility is to be trapped behind a cave-in without anyone knowing you are there. Death may come through starvation, thirst, or gradual suffocation.