Edit Note: I am thankful to anonymous who has made following comments on July 2, 2009.
The Katoomba Scenic Railway doesn't actually descend into a mine.
The town of Katoomba is located at the top of the cliff on a plateau.
The funicular serviced mines that were located in the base of the cliffs. The coal was brought up the cliff and transferred to trains for transportation to other areas.
The rails descend through a narrow crack in the rock which was widened out into a tunnel. The top and bottom are both in open air.