The castle is located on a hill so that you have a nice view from there over the city.
Here is plan how the castle looks from the inside. Since they charge a quite high admission fee we did not enter it but as you can see the castle is quite big!
And like this it looks from down the hill and by night
On the left hand side we had a nice view over the roofs of Edinburgh
Looking down from the other side we even saw the sea since Edinburgh is located at the North Sea