That's Moat Cailin.
Game of Thrones Season 5, Episode 3
I wanted to trade him for Moat Cailin.
Game of Thrones Season 4, Episode 2
The Starks will have dominion
over all lands north of Moat Cailin,
Game of Thrones Season 2, Episode 5
Go back to Moat Cailin.
Game of Thrones Season 6, Episode 5
Bring me Moat Cailin.
Game of Thrones Season 4, Episode 8