This is on the White Pass and Yukon Route railway outside Skagway. If you ever get a chance to visit this part of Alaska I recommend an excursion on the White Pass. It winds its way up a mountain range from the sea with spectacular scenery at every turn.
The best part for me is that each car has an outside platform where I could stand and take photos. I hardly sat in my seat the entire three hours. On the way up we were in the first car behind the engine. When reached the pass at the top of the mountain we pulled onto a siding where the engine relocated to the other end of the train. Now heading down the mountain I had an unobstructed view out the back of the train. This was one of a couple of tunnels high up the mountain.
There's nothing quite like traveling through a tunnel on a train. This one is near the top of the mountain so when you come out the other end there are amazing vistas. As we were on the last car I shot this looking back as the entrance receded into darkness. In the next moment we came out along a high slope where we could see dozens of miles out to the sea below. Put this one on your list of things you must do.