For this achievement you simply need to complete the mission, Chain on Fire on any difficulty. This can be found in the Karak Azgaraz DLC section of missions.
The objectives are quite simple.
- Head to the bridge and pull the lever to bring the bridge down. On easy difficulty the bridge will stall once and you will need to pull the lever again.
- Next you'll climb the mountain and head toward the beacon.
- Once at the beacon you'll need to stand on the pressure plate to fill the pipes with gas and to light the beacon. You can also unlock if you never step off the plate during the whole ignition process.
- After the beacon is lit a small hole will appear and it's a quick downhill sprint to the cart.