Kill the Twins [30G]

Location: Pinai Ferry Station
You will reach this location about halfway through the game while following the main story quests. You can also fast travel to this location later on. To unlock the achievement you need to kill two special gas zombies. The first one is located at the beach in the northern part of the map. He is easy to see and will attack on sight. The second one is a little harder to find. He is located in the southern part of the map and you need to climb a hidden ladder to make him appear. The ladder is behind a sign that says "Workshop". The gas zombie is trapped in the workshop garage and will only come out after you have climbed the ladder.