To unlock the "Abysmal Covenant" achievement, you must discover the "Pilgrims of Dark"
In order to do so, you have to speak to Darkdiver Grandahl
in his 3 locations in no particular order.
Here are his locations:Shaded Ruins
- Before taking a left to head to the fog door path. Keep going forward into the tall grass with the 3 trees. There is a trap hole you need to fall down where you will find Darkdiver Grandahl.Black Gulch
- There are two worms that come out of the wall. You need to fall down onto a ledge in between the two holes in the walls. You will find a locked door. If you keep going further down, you will find
that will drop the key to the door. Take the cage elevator back up, drop down and open the door to find Darkdiver Grandahl.Drangelic Castle
- After finding the first bonfire in the castle. You will be in a room with six doors and a lot of stone soldiers. Killing them near the doors will open it. The door to the far left has a hole you need to fall into. You will find a bonfire and if you keep going you will find Darkdiver Grandahl.
After talking to him all 3 times. You should be able to join the covenant and gain the achievement!