I found the other guide very hard to follow so I have added my own.
Firstly make sure you are in The Hinterlands.
Fast Travel to Outskirts Camp.
If, for whatever reason, you cannot fast travel there then simply find it on the map, Mark it and make your way there. Just above the camp and over to the right a bit you will see a cave icon, hover over it on the map and you will notice that it is a dungeon. Go to this dungeon and you will have no trouble unlocking the achievement. I got it within seconds of exploring the dungeon.