a very, very bad place
One disturbing aspect about this particular tunnel was the lack of airflow. If you spend much time below ground, you become pretty aware of the movement of air around you (or the lack thereof).
Just a couple of feet in front of where this picture was taken, the air quality became bad - probably because of the offgassing of those timbers. Oh ya, being anywhere near a tunnel whose roof is held up by timbers of uncertain age and stability is also a bad idea.
There's really nothing about this place that is a good idea, ok :-)