You have discovered a peculiar lightstone, which are commonly found on the corpses of wisps. This one is emanating with a strange light, however. Could it be somehow related to the Knights of Truth that used to inhabit this region?
The entrance is at ( -4, -48, 729 ) /waypoint -4, -48, 729
In order to enter Bloodskull Valley: Maulic's Stronghold, all group or raid members must talk to Amulius Ramio at ( 24, -46, 725 ) /waypoint 24, -46, 725. He is crouching behind a big rock just outside the Bloodskull Valley entrance. Hail him until he goes through his entire dialog. This may entail talking to him two times or more, depending on the conversational choices you make.
Drull is in the fourth wave of a horde of level 22 and 22v, they come in large groups of 5-10 it seems. More will aggro after a specific time. If you die, it does not take you out of the instance, keep hacking away until the General shows up. His death is the only step needed - completing the entire instance is not required.
Important note: There is a 12 hour lockout timer for this zone. If you leave before killing General Drull you will need to speak to Amulius Rami after the 12 lockout passes to regain entrance.
Speak to Cannix. A group of one Lucanic Knight Initiate and two a Militia guard will spawn, kill Cannix, and then (if they're not gray to you) attack you. You must kill them to complete the quest even if they're gray.
Note: You must wait for the soldiers to kill Cannix first. Cannix is no longer attackable and the Lucanic Knight and his guards are non-aggro. Just step back and let them kill Cannix, then kill them to complete the quest. If you kill the knight and guards first, just talk to Cannix to get them to re-spawn.