I saw a movie on TV in 1992 or 1993 that prominently featured a train depot that was hidden inside of a mountain. I believe the depot was the main hideout of the 'good guys' in the film.
The depot was marked by an 'end of line' maker on the tracks consisting of a wooden board with some 'caution' markings on it. When the characters wanted to enter, they would drive the train up to this marker, somehow communicate with staff inside, at which point the false front of the mountain would slide to the side. The marker was attached to the facade, so it would side along with the rest of the mountain so that the train could enter.
I'm not sure of the time period, but they were definitely using steam engines.
There may have been supernatural or fantasy-tech elements, but I can't remember much beyond the hidden train depot.