Kill Sentry Goorlux. Kill the 38^^^ wandering placeholder, a Deathfist sentry, that randomly spawns during the daytime in the wilderness near ( -201, -18, -330 ) /waypoint -201, -18, -330. Both the named and the placeholder spawn between 6 and 8 minutes and moves very quickly. (which helps you spot him!) Sentry Goorlux will despawn after a while.
Known spawn locations of the placeholder:
At the tree stump on the right between the mill and the Titan Tower
Near the Tree stump between the brigde and Titan Tower
Go back towards the Deathfist Jail area, then go down another flight of steps and through some double doors, into the viewing area for the gladiatorial arena. Move around the arena until you find the doors to Fyst's private box. From here you can jump down into the arena..
After everyone is in the arena, click the gong and, after being addressed by Fyst, The Harrower of Zek will spawn. He is a level 40-42 Heroic mob. He has horrible knockback - try to keep your back against the wall near the locked exit gate and the damage from this is minimised.