Take the path that heads south and slightly east out of the town of Morthal. Once on the road turn left (or east) and walk a few feet. On the left, just past the hill that leads to Morthal, is the Nordic burial site.
Inside is a necromancer impaled to a table by a dagger. The powerful Staff of Revenants can be found near his body. There's an animated skeleton to eliminate, but then there is some loot to collect in this ruined barrow.