Just a quick little shop some people may miss where you can get a key, halberd and another life flask.
Now I'm not sure if I unlocked this through a boss battle, or possibly through one of the post release updates, but the first time I was here there was no shop at all. You may need to see the Temple of Ur first.
EIther way, once you claw your way out of filth Hell, make your way all the way to the right of the boneyard.
Find the elevator that goes down.
Slaughter your way to the right...
...until you get to the *first* elevator on the way right, and take it up.
Now you should be on this side of the map. I know it's simple, just trying to help
Here you will find the grave digger. If you talk to him from the left side, he'll just give you dialogue, but talk to him from the right and he'll bring up his inventory.
Buy whatever you like/want/need, and if you don't, well, he thinks that you are.