Muncaster Castle is a privately owned castle overlooking the River Esk, about a mile east of the west-coastal town of Ravenglass in Cumbria, England. It is recorded in the National Heritage List for England as a designated Grade I listed building.

The River Esk, sometimes called the Cumbrian Esk, is a river in Cumbria, England. It flows for approximately 25 km from its source in the Scafells range of mountains to its estuary at Ravenglass. The valley it flows through is known as Eskdale. It is one of two Rivers Esk in Cumbria, and not to be confused with the Border Esk which flows into Cumbria from Scotland.