The Ghost of Old Hroldan

Walkthrough
While at the Old Hroldan inn, the Dragonborn can rent Tiber Septim's room for the night. Doing so and sleeping there will cause a ghost to appear in the inn. The ghost mistakes the Dragonborn for "Hjalti" and says he has been waiting all this time for Hjalti to make good on his promise and bring him a sword.

Bring Hjalti's Sword to the Ghost of Old Hroldan
The Dragonborn can then ask Eydis about the story and she will direct to one of the following dungeons:


 * Broken Tower Redoubt
 * Bruca's Leap Redoubt
 * Deepwood Redoubt
 * Dragon Bridge Overlook
 * Druadach Redoubt
 * Hag Rock Redoubt
 * Red Eagle Redoubt
 * Serpent's Bluff Redoubt

It is then simply a matter of going to the specified dungeon and retrieving the sword, then return to the inn and give it to the ghost.