ToME: the Tales of Maj'Eyal

I'm something of a ToME newbie - where would I go to get that addon?

I've completely cleared out dreadfell, and have even dug around a bit, but I can't find the boss. I've opened all the vaults and killed all the monsters, save for a level 51 forge giant that's just a wee bit too much for me at the moment. But I get to the bottom floor, with nothing else to find and ...