The Citadel: Prophecies

II: 382 - The Sea

"It is the sea that comes."
"The sea?"
"I dreamed that the sea was lapping all around Winterfell. I saw the black waves crashing against the gates and towers, and then the salt water came flowing over the walls and filled the castle. Drowned men were floating in the yard. When I first dreamed the dream, back at Greywater, I didn't know their faces, but now I do. That Alebelly is one, the guard who called our names at the feast. Your septon's another. Your smith as well."

This was fulfilled by the capture of Winterfell by Theon Greyjoy.