Next time I'll be visiting Edinburgh I'll probably check Millie's availability before getting the actual plane ticket. The house is absolutely perfect for two people and superclean. All the facilities were there and working well and we even had some biscuits waiting for us upon arrival. The location is just a short climb of the castle and easily accesible with public transport. Grassmarket with all it's pubs is around the corner and, for the booklovers amongst us, there are three bookstores in the same street.
Millie's BnB made our stay so much easier and she was the absolute sweetest in checking if we made it okay and if we had a good time.
Last fun fact: quickest way to the Royal Mile from the appartment is walking up the actual Diagon Ally.