I believe you are referring to Kilchurn Castle, which is located on a rocky peninsula at the northeastern end of Loch Awe in Argyll and Bute, Scotland. It was first constructed in the mid-15th century as the base for the Campbells of Glenorchy, who extended both the castle and their territory in the area over the next 150 years. After the Campbells became Earls of Breadalbane and moved to Taymouth Castle, Kilchurn fell out of use and was in ruins by 1770. It is now in the care of Historic Environment Scotland and is open to the public in summer 1.
If you are interested in exploring more abandoned mansions in Scotland, you might want to check out Glamis Castle in Angus, Scotland. It is known for its haunted reputation and has been featured in several books and movies. Another option is Culzean Castle, which is located on the Ayrshire coast and is known for its picturesque views and impressive architecture