"Winterfell's in the midst of a frozen field," Sansa explains.

"There's no mountains nearby and the closest lake is leagues and leagues away. It's got high walls, though, and it can withstand a decent siege. It's just hard to get to it from the south, you see, because there's a very narrow neck of land that's marsh and swamp - few armies can cross it to make it north to begin with. I think my ancestors relied too heavily upon the Neck and didn't shore up defenses elsewise."