I've already taught on of my friends how to do it. 1. Set down 2 Stone Bridges vertically right next to each other, so if you were up in the air looking down on them, they would look like ||. 2. Set one of them to not place at the start. ||<-not at start 3. Start a new round. 4. Remember which side of the stone bridge which they were touching! Now, place a two way node or sender (depending if you want a 1 way door or an in and out door) and wait (or instantly spawn) the bridge. 5. Delete the bridge that doesn't have the door in it, and you're done!
I think it's just Foundry. But If you're having so much trouble on it than it probably can't be done. EDIT: Nvm,