Instead of just cave on one Hex, you would enter another world. The underworld.
That means, another board.

this would allow

* More connexion with the regular board (upworld)
* interactions between up and downworld (with various levels for going deeper)
* Dungeons style adventure (yes, with traps)
* An open ended board (the underworld would be discovered as you go)

It could be almost a game on its own.
In the "extension" mode, it should be more limited.

Ideas ? Anyone who'd want to lead this thread

Completamente de acuerdo. sobre todo en cuanto à las trampas !
Perso, igual que todas las extensiones, mejor lo dejarmos para cuando el CORE este solido, no ?