How to get Magebane - Elder Scrolls: Morrowind
Location: Urshilaku Burial Caverns
Video: How to get Magebane
Magebane is an Artifact Weapon which you can find in the Urshilaku Burial Caverns, a dungeon you'll be visiting during the Meet Sul-Matuul Story Quest. Since this is an Elder Scrolls game you can technically come here at any point during the game and pick up the Magebane weapon - you don't have to be on the primary quest.
For help locating the Urshilaku Burial Caverns check out my map location below. This dungeon is almost directly north of Maar Gan but there will be many mountains in your way if you try to take this route. It's usually easiest to run to the Urshilaku Camp first then travel a little bit south to the burial caverns.
You can find the Magebane in the Laterus Burial section of this dungeon, it's the large room with a very high ceiling and many narrow stone bridges that will take you up. Along the way up you'll find many doors which shoot off to other burial chambers too.
To reach Magebane what you're going to want to do is head on up to the top of the cave and Levitate southeast towards all of the Mummys along the wall. When you get to the Mummys turn around and look back in the direction you came from, you'll see Magebane a little bit below you (pictured below).