Hmmm...

I see this as an event with two Pages and the lovely little Preconditions:

Event Page 1

Nuffink whatsoever. Not even a picture. Can't be activated either.

Event Page 2

Precondition - switch [0001] ON.

So this event will have a picture of, say, stairs leading into the ground. And when the Hero stands on it, they get teleported to the next map - ie. The dungeon.

I can make a little demo if you want.

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EDIT: And here it is. Quick little thing. You should know what to do with it.