Going through the tunnel there was a long sound, mostly like an old steam train whistle but also a bit like a high-pitched shriek. And then, an unattended child disappearing. By the time I woke up from the dream, I'd discovered that dwarves were responsible - the old kind of dwarves who're cunning smiths and play nasty tricks on miners who don't leave food out for them. I don't know why they wanted children, but a few of the staff on the train were in league with them and being paid off to look the other way. They might have been smuggling other things on the train, too. There were a lot of bags being unloaded on the wrong side of the platform, only some of them struggling.
I have no idea why or how my brain came to this idea. It sounds a bit like something from the same kind of modern folklore storyworld as Ночной дозор (Night Watch), The Dresden Files or possibly Hellboy à la Del Toro. I don't know. Maybe someone can work the idea into a modern horror story or game, somewhere.
It'll be a hot shower and an early night tonight, I think.