Here is the full list of all 14 Castle Torgeath: Descent into Darkness achievements.
You completed the game in Normal Mode
You completed the game in Rogue Mode
You completed the game in Hard Mode
You successfully completed Level Six
You killed the Arch Demon in Level Six
You successfully completed Level Five
You killed the Golem in Level Five
You successfully completed Level Four
You killed the Orc King in Level Four
You successfully completed Level Three
You killed the Orc General in Level Three
You successfully completed Level Two
You successfully completed Level One
You killed the Spider Boss in Level One