Taking out the trash Achievement
Taking out the trash20
Defeat the rock golem guardian.
Unlocks within BURIED PASSAGE
To save you a LOT of frustration, here's the easiest way to do this: first and foremost, make sure that when the big rock guardian throws a rock at you, that you don't let it hit you, because more than likely you will get one 'shotted'. It has a super cheap area of effect as well when it hits the ground.
To make this much easier, simply jump as soon as the rock is about to land near you, and it will never do damage to you. This will save you so many deaths. Secondly, take out the floating rock spawners so they stop spawning guys. Then when it's only you and the rock guardian left, just keep shooting him with the wind charm while avoiding his rock throw. Also make sure not to get too close to him for long because he stomps the ground. I found using my sword to be the best method here for the normal guys.