Edinburgh Castle is the most important tourist attraction of the city. For centuries the castle was the seat of Scottish Kings, today it is the headquarter for the Scottish Division. Edinburgh Castle is located on a volcanic rock and dominates the skyline of the city. A visit can take up to 3 hours, but it's well worth it.
The big cannon that you see on the last photo is called Mons Meg. It weighs 6 ton and last saw action in 1681.