What would you do if you were on an underground train, when suddenly the train shook, you passed through a portal, and the next thing you knew your carriage was lying in an unknown new world?

Edit: apparently this is a very common form of Japanese storytelling called an isekai. There are 8 billion people in this world, no idea can be original. And sometimes you miss out on things many other people know. I'm clearly one of today's lucky 10000.