Fly to Southshore in Hillsbrad Foothills.
Run north-northwest to Alterac Mountains.
Pass just east of Dalaran, to Lordamere Lake.
Swim north, until you hit Tirisfal Glades.
Find the road just west of the Undercity. (East of the Undercity is all cliffs and you won't be able to get past there.)
Run north and east to the Scarlet Monastery, avoiding the guards at Brill. Just past Brill, the road goes southeast, but there is a smaller path going northeast, to the monastery. There will be corpses hanging from trees when you get close.