Upon completing the Pillar Puzzle while attempting to work your way through the Clotted Avenues quest in Graven, you’ll receive the Turtle Key. Each of the keys you’ve found so far has a corresponding door that you need to use it on, opening up the next area for you to advance. Up until this point, a majority of the doors have been pretty straightforward and easy to find. The Turtle Key door is a little tricky. However, the developers are giving you a hint of where to look based on the name of the key.
Rather than looking above ground, you want to look below it, primarily in the water. Nearby the pillar puzzle, close to the entrance you entered for the area, there’s a small doorway you can take that opens up to a massive pool. There are several eels in this area, and we’re going to recommend you clear them out from the pool.
Once the eels are all removed, make your way to the center of the water and dive into it. You’ll find a sewer grate when you dive down a little bit and sticking out if it is the distinctly white silhouette of a key. You’ll need to use the Turtle Key on it, so make sure you have that in your inventory.
The sewer grate opens after you insert the key inside the door, and you can proceed through this area to next the location for the Clotted Avenues quest. You’ll be returning to this pool not too far in the future.