After Warcraft III, the Kirin Tor raised a barrier to conceal Dalaran's restoration in the Alterac Mountains, but the barrier is down. Inside, enchantments backfire, arcane constructs go haywire, demonic energy runs rampant and there are cats everywhere (“I guess that part's normal”). Those who help may earn magical artifacts.
Blizzard hasn't published the bosses yet. We'll add them as soon as they're known (the beta starts on September 17).