C16 castle built from monastery stone for Bishop of Argyll on east coast of Kintyre. You can actually stay in the castle courtesy of Landmark Trust.
The castle was built at the start of C16 and then passed through various hands before being sacked in 1558 by Mary I (of England) It was rebuilt afterwards before falling into disrepair around 1750s. It was bought by the Landdmark Trust who restored it as self-catering accommodation (see link).
The location beside the shore is really splendid and it is well worth a quick look and then stopping by the seashore as well.