Settings: Riverrun and Riverlands
The Riverlands is located in the middle of Westeros, and is an extremely fertile land due to the many rivers that run across its expanse. It has been conquered more than a handful of times in the past, but it is presently under the rule of House Tully. Riverrun is the ancestral home of the Tullys, and it comes with a unique defensive mechanism: sluice gates can be open to flood a channel on the west side of the castle, turning Riverrun into an island. An invading army wanting to hold Riverrun at siege would have to separate their army into three different parts to place them around the castle in order to prevent supplies and reinforcements from coming in.