Map showing the location of Karhold on the continent of Westeros.
Karhold is the seat of House Karstark, a vassal house holding fealty to House Stark of Winterfell. It is located in the far east of the North, south of the Bay of Seals and inland from the coast of the Shivering Sea.
The castle was founded by Karlon Stark, a younger son of the then-Lord of Winterfell. The castle was then called 'Karl's Hold'. He was rewarded by his father for putting down a rebellion by House Bolton of the Dreadfort. Over the centuries Karl's Hold became Karhold, and the Karl's Hold Starks became House Karstark.[1][2]
In the books
In the Song of Ice and Fire novels Karhold's position is the same and House Karstark remain amongst the Stark's strongest and most loyal supporters.