On a Youtube Kick tonight, haha. Anyhoo.
Montana Rail Link's summit tunnel of Mullan Pass (summit is actually a few feet behind the video camera. At the time this was shot, helper crews had to wear oxygen masks (like a scuba tank/mask), you'll see why. In 2009-2010 MRL demolished this side of the tunnel and a scene like this is no longer possible.
http://www.youtube.com/watch?v=v-ECBxoJqYE