man rappelling down the interior of a large, smooth, sloping concrete structure

man rappelling down the interior of a large, smooth, sloping concrete structure. The man is wearing a safety helmet with lights, a black jumpsuit, and a harness connected to blue and yellow ropes. He is holding what appears to be a measuring device and appears to be communicating with someone using a microphone attached to his helmet. The concrete slope has streaks and stains running downwards, suggesting the presence of moisture or previous water flow. At the top of the slope, there is an opening, likely the exit of the tunnel. The camera follows the man as he descends, maintaining a focus on his movements and the surrounding concrete environment.