Perched on castle rock above the old town, Edinburgh Castle is one of Scotland's iconic images and a must-see if you're visiting the city. Your problem will be time - the place is huge and there is a lot to see and take in. The castle was at the centre of the wars with the English and, as well as being a fortress has been a prison, Royal Palace and garrison. It was the birthplace of James VI who, as James I of England, became the first monarch of both countries in 1603.
Castle Rock was used in the Iron Age, but there is no evidence of a stronghold until the 7th century. The oldest building there now (and in Edinburgh) is the 12th century chapel dedicated to St Margaret, built by her son, David I, in his mother's memory. The Castle also includes several museums - for example the National War Museum and various regimental museums. Not to be missed - the Honours (Crown Jewels) of Scotland.