There's a train station that can only be accessed in dreams. When you go there you can choose to go to another reality. Of course, since you're still a person when you take a train to another reality you don't physically go there, you wake up as yourself in that reality. Depending on the situation that can mean you'll have a very diffrent body or life wherever you go. And the version of you from that other reality will have to deal with being swapped as well for better or for worse.
People are able to freely choose where they go if they get to the station. But every trip is risky as it's very very unlikely anyone who goes to the station will ever see it again. Once you go on that train you have to be prepared to live the rest of your life in a completely diffrent reality from the one you grew up in. So be careful.
A train is exiting the station right now, let's see where it's going.