There are 55 quests that should be completed to obtain this achievement if you are like me and had 54, chances are you played online and experienced a glitch that didn't count the quest "violent goblins".
This is the 6th quest for me and should be the first few you get in the game.
So if your game didn't count it then you will have to start a new character. Make sure you don't go online or join someone's game during the beginning so you don't get screwed.
Other than that the last quest is for floating gardens on normal. You should do this with preferably a gunner and also a partner.
Update- just got it with my friend and we both had this as our last quest. so if this is your last quest then you can play with someone on their file and get this :)