At the end of the underground line the train would disappear, and a new train would be made out of thin air to follow on the opposite direction.
A childhood belief about trains

others believed things like this
- i used to believe that if you put a penny on a train tracks that it would derail it — ROSS
- For some reason, I used to believe that women only got raped on train tracks.
— Jessica Tinch - If you click a pen to much you will disappear Anon
- i used to believe when someone died their image on photo's would disappear— beryl's girl
- I used to believe that the sky is just a very thin blue egg shell— Alan
- I used to believe that when people died, they vanished into thin air. — KJ