It's a really sweet area, look's a lot like a land torn apart by earthquakes and violent storms before being torn out of the ground. Windswept and desolate, it's a massive mismatch of terrain, with mesas, cliffs, and epic vista points all filled with scattered blocks of pure iron, gold, and even some diamond. Topped off with a shrine and a poetic gift; "You have done well to have come this far fellow crafter of the mines. I bestow upon you the near unbreakable HEAVENLY DIAMOND KIT Use it wisely. And most of all DON’T LOSE THEM FROM A FALL!!!” right next to a canyon leading straight to the void that’s divides the whole floating island.
But yeah, me and some of my buddies played for a good long while using this map on our server. And I have to admit, it's pretty awesome. Hope someone will eventually make another (even better) version of this.
so after a while exploring the areas around Helldam islands, i went to accension woods. Found the dungeon, currently trying to make my way through with 2 diamond swords and a suit of diamond armor. Helldam islands is full of diamonds!