Anyway this is something I discovered lately. I left the grid up for locating purposes.

Right around that area are a bunch of squares connected in a bit of a zigzag that if I have the gravedigger's flame spell active and stand in one of those spots the fog overlay turns a creepy blood red.
For clarification purposes I currently have the *ahem* appropriate amulet equipped.
Not that it would be much of a spoiler to mention specifically really, but I like being all mysterious and obfuscative.

Edit: Startling new developments!
At X=15 Y=80 on the same map I found another spot and encountered an Acid grub.
The overlay would alternate between red and normal as the grub and I traded blows. That was entertaining.
