There's an old story told to foals about a train that goes to every place in the universe that ponies can imagine, and even more places that they can't imagine. It's a train that arrives only once a lifetime. It's a train that picks up lost souls and carries them to other realms.
Those stories say that if a pony rides it all the way to the final stop, they learn the secret that all alicorns know.
Inspired by Galaxy Express 999. Updated irregularly.