My scout reports that a large force of cultists just marched north into the Shadowgale forest. Other than the pylon, there isn't much there of interest. Head north into the forest and catch up with them, but give the shrine a wide berth for now. Take as many of the cultists out as possible once you reach the Shadowgale and try to determine why they are there. These cultists aren't much for thinking for themselves so taking out their commander can generally cause them to crumble quickly.