Mortrag Peak

is one of the highest points on Solstheim, east of Northshore Landing. 
The location only becomes unlocked on the map when the Dragonborn climbs right up to the very top. There is nothing much up here, other than the view, and the location is not connected to any quest.
Note: Judicious jumping may be enough to get up there, though riding a horse is supposed to work better.
Category:Dragonborn DLC locations
Category:Points of Interest