Dragon Age: Origins

This secret achievement, "Keeper of the Vigil", is one of 5 secret achievements in the Awakening expansion pack. It is 1 of only 2 missable achievements (if you are planning on getting them all in 1 play-through a tactical save is required) and works in a similar choice system as all the main faction choices in the original game. When you have completed the three storyline quests, located in The Blackmarsh, Wending Wood (Silvrite Mine) and Knotwood Hills (Kal'Hirol) and you return to the Throne Room of Vigil's Keep the nobles will be gathered and Seneschal Varel will give you a typical 'point of no return' speech. Here you will be given 2 dialogue options:

1.) Assembe the men. We're going to war.
2.) There are some things i must take care of first.

If you choose the second option you are free to return to your game. If you select the first then you are tied in to finishing the game. When you choose option one you have the choice of choosing your end-game party and then it's off to Amaranthine.

When you arive you will fight a bunch of darkspawn and some grubs. Kill them and the city's defenders will start a conversation with you. As this is happening a talking darkspawn representing The Architecht will approach and inform you that The Mother's forces are marching on the Vigil. This is where your choice affects the achievement. Again you have 2 choices:

1.) So be it. destroy the city.
2.) I'm not giving up on Amaranthine.

Choose the first option and you will set the city aflame killing all the darkspawn and residents alike. You then head back to The Vigil and get the option of re-choosing your party. Select whoever you want and then its battle time. I am assuming you have taken the time to build the upgrades to the keep when doing this quick runthrough (as most items you need are all picked up in the story quest areas). First head to the front gates and dispatch the darkspawn there. Secondly you will route a group of Children attacking the east wall. Fight your way through the courtyard to the front gates once again and dispatch any enemies here. When this is done you will head to the courtyard to fight a group of Heretic Disciples and after them an Armored Ogre Alpha. When he falls head to the front gates to kill The Herald and the achievement is yours.

This achievement is missable if you don't save at the right moment and choose the other path. Save your game just before going to Amaranthine to fight the darkspawn at the end of the game.

Upon arriving at Amaranthine, you will fight a small group of darkspawn, and immediately after, a cutscene will trigger and you will have the choice to stay and defend the city, or come back to Vigil's Keep. Choose the latter, and you will find yourself back at your fortress. Successfully defend it and you will earn the achievement.

Reload your save and take the other path to get "Amaranthine's Last Hope" achievement.