This achievement is part of the Dawnguard story so it's near impossible to miss.
*Minor SPOILERS ahead*
Just finish the first mission given by Isran in Fort Dawnguard, you get the achievement right after you meet Serana.
*BIGGER SPOILERS AHEAD*
If you're not sure how to start the Dawnguard DLC first you need to be at least a level 10, after that simply ask around ANY town for rumors (the guards are best for this) at which point someone will mention how vampires are starting to become a problem or how the Dawnguard is being rebuilt and they're recruiting people. The game will hint you Riften, so go there and ask around again.
After that you will get a message saying "Started: Dawnguard" and a marker will appear just north of Riften. Follow the quest marker and along the way you will have to fight random vampires/vampire creatures until you get to a cave. Keep following the quest marker until you arrive at Fort Dawnguard and talk to Isran and he will let you join the Dawnguard (don't worry, you can still become and join the vampires) and give you a quest to find out what some vampires are up to.
The mission will take you to Dimhollow Cavern (which is just south-southwest of Dawnstar and just a few feet north of the Lord Stone). In this cavern you will encounter vampires and vampire hounds so be prepared! The very first section has a locked gate, just look across the gate and there's a sort of balcony, go to that balcony and there's a lever you can pull to open up the gate. After that section there's another section which has these sort of 'jailed hallways' if you look around you will notice that there are weapons and potions behind these fences but you cannot reach them. Use your newly acquired crossbow (or any bow for that matter) and shoot the weapons and/or potions to get them closer to you if you're so inclined to have them. I skipped them because they're kind of weak, but might be more useful for lower ranked players.
Anyhow, continue following the cave until you come across a circular platform which has a little stand in the very middle, get closet o it and push the button after which these purple flames will show up and then it becomes a puzzle where you have to push these braziers. The point here is to follow the flame and push the braziers so that they meet with the purple flame so that the braziers light up (it's not that complicated, trust me). After you've done that, this crypt will rise out of the middle so get close to it and activate it. It will open up and a character Serana will come out and you talk to her. Talk to her and the achievement should pop up.