The Ancient Helmet of the Unburned is a unique Ancient Nord Helmet. When worn, it provides a 40% resistance to fire damage. Its appearance is exactly the same as the Ancient Nord Helmet and it can be improved with an iron ingot.
This helmet is unique in the fact that it provides elemental resistance, while being an item worn on the players head. Elemental resistances are usually limited to Shields, Boots, Rings, and Amulets.
Location
You can find it in a corner behind a locked gate in the Labyrinthian Tribune, during The Staff of Magnus quest line.