Battle Tankard

Irina's happy to give you a Battle Tankard once you finish Days of Wine and Stealing side quest.

In-game description
"This enormous tankard seems sized for a giant. Indeed, a rune on the tankard's base indicates it may come from the halls of Gerti Orelsdottr far to the north. Someone has carved eye and mouth holes in the tankard's side so it can be used as a helmet. Wine stains and the pervasive smell of stale beer indicate that the wearer of this "helmet" is used to reveling late into the night (or perhaps early into the morning)."