This is a fabulous place. David is a great host, couldn't be more helpful and welcoming and a source of knowledge of the history of the place which was a real added extra layer to the staying in the apartment. The location could not be better - you are literally at the top of the Royal Mile and next to the entrance to the Castle. Everything we went to was walkable, mostly within 10 minutes. The views are outstanding, and the apartment is not only very spacious but also beautiful with lots of original features.
There are a few things to be aware of if coming. Firstly, it is not only up four flights of stairs, these are spiral (large spiral, not awkward), and they themselves start at the top of quite a steep hill, and quite likely having arrived into the courtyard, which is several flights of steps down from the entrance door. You do need to be fairly fit to stay here, and I would advise thinking carefully about luggage! I strongly recommend booking an online shopping delivery before arrival, as the delivery driver will then bring it up for you which saves another trip, especially if you arrive by train as it's a bit of a walk to find anywhere selling normal groceries. You do find yourself getting used to the stairs even on a short stay, but the warnings about accessibility are absolutely to be taken seriously.
Secondly, the location, whilst amazing, does mean that for a good chunk of the year you are not only next to the Castle, which is amazing, but next to some full on scaffolding building works. These had begun by the time of our stay on 12th May, so I would say anytime in May onwards you are likely to find this. The works take place every single day and start at 7am - you will be woken in the rooms facing the Castle. It's interesting to watch, but they are extremely close to the flat windows, so you are overlooked during the day, every day. If you want to avoid this I would recommend booking no later than April. Of course if you are interested in large scale construction work, then it adds a rather unique excitement to the trip!
David was very helpful throughout the trip with a few on-going queries, and very helpful when we managed to forget something too! I highly recommend staying here, it's a unique way to see Edinburgh and makes you feel a little part of it's history.