Credit to @Rusty for this guide!
First, make your 3D map. Use layers to make it more realistic!
Now, make a ladder either with a bicycle rack or wooden poles.
Place three invisible teleporters, first one teleports there on tp1, second on tp2, third tp3, like this:
Now, make four triggers, the first one transmitting on tp1, the 2nd and 3rd on tp2, and the fourth on tp3.
Put a button at the bottom of your ladder, and wire it to Trigger 2, then to Trigger 4. Wire a button at the top of your ladder to Trigger 3, then Trigger 1.
Have fun!
-@Blizzy