Event: Walder Frey - Acquire a New Castle/City/Army/Loot (Political Wins)

Episode 10: The Winds of Winter at 22:30
Ownership of Riverrun transfers back to Walder Frey after the Lannister army helps to retake it from the Blackfish.
Walder Frey: "Riverrun belonged to House Tully for a thousand years. Now it's mine. What do you call that? Victory."
(Acquire a New Castle/City/Army/Loot)