Grassblade was aghast to hear how the life energies of his Green Hood comrades who fell when Deathfist Citadel was retaken by the Deathfist forces, have somehow been stopped from rejoining the life flow. Being an accomplished burglar, he has volunteered to not only show me how to gain access to Scourge Keep, but to also help me solve this mystery.
Enter Scourge Keep by clicking the sewer entrance beneath the Bridge of Zek (-210, -25, -538).
The entrance is underwater at ( -193, -36, -579 ) /waypoint -192.61, -36.12, -579.35
In order to gain entrance to the Keep, you will need to swim around the moat until you get the brief cinematic, then kill Viletooth (crocodile) in the north end of the moat. Then you can access the sewers.