Ok, I'll bite -- you'll need to improve the lighting inside the tunnel. The shot of the actors in the tunnel back lit by the exit is good - so was the shot of the person lying on the ground. Both are good examples of using extreme contrast to convey darkness. The other footage in the tunnel was not -- we could not see anything and would be an excellent reason to quit watching the video. You don't have to light the entire tunnel -- just provide enough light to provide a lot of contrast to the image. Even if we don't know exactly what we're seeing, at least there is an image to look at.
Good luck.