Razorfen Downs is a mid-level, difficult instance dungeon situated on the south end of The Barrens. To reach the entrance of the dungeon, take the eastern 'fork' near the Great Lift. The dungeon entrance is on the southeastern end of the maze of quillboars there.
The instance dungeon itself is filled with undead quillboars, quillboar necromancers and the scourge itself. The southern end of Razorfen Kraul has a spiraling hillside filled with undead, the 'Spiral of Thorns' has the lich at the top. In the northern region, there is the bone pile which must be experienced first hand. Preferably with an organized group.
Most of the undead come in pulls of four-or-more. Skeletal Summoners summon in more undead, the ghouls hit you with a 10 minute 10% accuracy debuff and the freezing spirits will frequently root.
The treasure drops are not particularly great given the difficulty, and there doesn't seem to be a lot of quests for this dungeon, but it is so thematicly cool it's worth at least one visit.