Start the quest and take the portal to Cemetry of the Forsaken.
Walk north-west, through the gate to the Fields of Misery.
Stay at the left side of the map and go up.
After 30 secs you should see the den already, if not walk to the middle of the map.
Still not there then its all the way up, I'd restart the quest because its too long walking.
Inside the den run to the zealots and kill them, because of their low defense they die pretty easy.
Loot the magic or rare.
Continue the quest (46k) and get the glowing sword shard. Teleport to town, talk to cain and receive 17k xp. 63k xp total in maybe 2 minutes, depending on where the den is.
Im level 52 atm and I only need ~16 runs to level.