This is how it works: The only place where you can challange other players for duel is now Lorencia. After a duel challenge is accepted both players will be warped to the duel arena where they'll fight to death.
After the duel is over (canceled or someone won) you will be givven a 10 seconds time to warp to another map or you will be warped to the Volcano map.
From what I've seen the map is still empty, no monsters there, and I guess there should be some... it's kind of a large map, with lots of lava, and fire and stone. And few players.