We spent 4 days in Charlotte's flat in August and the location is fantastic for reaching all the festival's attraction.
The flat is situated at the 4th floor (without lift but isn't so difficult to climb!) of an old palace, it is big and clean, and the pictures really represent each rooms.
Charlotte is really a good host, she waited for us in front of the door and explained us the whole flat, she gave us suggestions for our time in edimburgh and she was always available by phone/mail for every problems. In addition she offered us wine, chocolate and breakfast meal for enjoy our holiday, we really appreciate her hospitality spirits!
In conclusion we strongly recommend this flat for your staying in Edinburgh!