Founded in 1128 and now the official residence of the Royal Family in Scotland. The oldest parts of the building is the most interesting with Mary Queen of Scots bedchamber and the adjoining room where her secretary was stabbed and killed.
If you interested in history, this will fascinate you along with the compulsory guided tour between November and March. During the summer you can just wander around. For art lovers don't miss the new Queen's Gallery.