An archetypal Pele Tower set in the heart of the Hunters land within view of the coast. Hunterston Castle was built as part of a medieval chain of castles to defend the west and south coast of Scotland from Viking invasion. The original Pele Tower was constructed in the 13th century from sandstone sourced on the Estate, replacing a previous wooden structure: this remains intact unlike other Pele Towers in the area. The ground floor is crowned with a barrel-vaulted roof which acts as a support to the stone foundation above.
Several features of the castle demonstrate that defence was foremost in the minds of the architects designing the castle, such as the wooden staircase to the main entrance could be removed if the castle fell under attack. In times of danger the ground floor room could be used to store food and animals and, in addition, a well was constructed to provide a source of water. The surrounding swamp made a moat unnecessary and acted as a good natural defence.
Hunterston Castle is thought to be the oldest of the local castles and the oldest castle in Scotland to still be in the possession of the family who originally built it. Buildings have been added at the side and rear to meet farming needs over the centuries. The Great Hall was added in the 16th century by the 14th Laird, John Hunter (up until that point the old hall had acted as the main living area). The 16th century also saw the addition of a stairway tower to give a ground floor entrance to the building, providing a comfortable staircase connecting the new Great Hall to the ground floor.