Here is the full list of all 10 Dungeons of the Fallen achievements.
Use Anvil to forge a new item
Defeat the Fallen Queen
Leave the Forgotten Cave
Get lvl 16 in a Ability School
Get lvl 16 in a Spell School
Find all Keys
Access Maulerum
Access Hoth Jungle
Defeat the Woodsman
Sit on the Lone Throne