Before the Cpt. Greenbeard boss fight and the shipwreck level, there's a run through the Piratopia. It's a short but hectic level.
After the shipwreck, we continue on into the Dwarven territory, and the first level there is industrial zone where dwarven forges and saws are, where stone is cut and... hammers are thrown. Unlike GnC1, this time hammer-throwing enemies hammers don't hone in into you, they just fly... toward a certain point. Also if a player is too low beneath their platform, they won't throw at all.
If you survive that, you actually get down under into the dwarven mines and halls, where even some unique Easter eggs can be found. Not gonna write any spoilers here, though.
This is the first underground area with real dwarves inside, as previous caves and mines were basically abandoned by them. There are constructs like flying security bot and similar remnants of previously technological civilization that is now trying to survive and live another day. After exiting this area, you'll end up on an ancient bridge that connects it to abandoned halls in the next mountain peak, where otherworldly things rule now and dwarves are no more... But they still hold the bridge, or at least part of it.
That's it for now. I've recently finished "Abandoned halls" level, which will introduce some new mechanics and will is an L sized underground maze. Following that, there's a third boss fight that is in testing phase right now...and that finishes the second third of the campaign map, thus making the latest build alpha3.