So, for this achievement, you need to reach the island of Kos, which is situated on the eastern side of the map. The recommended level is 34-34. Once you get to the island, you will notice a quest marker on the eastern side of it and it should be called "A Business Opportunity", it is located inside a fort and it requires that you free and carry Markos back to his place.
Once you get him back home safely, he will ask you to complete 3 extra quick quests and once you finish the 3rd one, you will unlock the achievement.
Hope it helps.