For more than 500 years, Inveraray Castle has housed the chieftain of one of the world’s best-known family clans, the Clan Campbell. It is now the home to the 13th Duke of Argyll, His Grace Torquhil Ian Campbell, and his young family. Visited by thousands every year, the castle was the stand-in for “Duneagle” in the “Downton Abbey” Christmas episode.