Since the codex doesn't have the locations marked for this, you need to go into the house on Wisdom Isle where the Giant's Heart vendor is, go down the stairs to the bottom floor, enter through the door that is there (can't remember how to unlock the ability to do so if you can't, I believe it's just questing on the island but could be wrong), and then you need to interact with the cubes in the screenshot below. Congrats on the achieve and title

Screenshot

Good luck with your achievement hunting!