Sofi's place is great! The location is *perfect*- I've stayed at other airbnbs who say they have a perfect location but this is the first that actually lives up to it's claim. If you just want to explore Gamla Stan it is great, but if you want easy access to the rest of the city it is central to everything and Stockholm's mass transit train is just across the street which will connect you with the cities buses & lightrail.
Access to the apartment is easy and secure, while it's true that the apartment is on the top floor and the stairs can be really cumbersome with luggage or after a full day of walking, so be prepared!
The internet is fast and reliable which is really nice if you're trying to work remotely while traveling.
Downstairs is Temple, one of the bars that stay open super late, which is great if you want a drink after hours because Gamla Stan shuts down at around 10 on weekday nights. Some reviews mention noise but we didn't actually hear too much coming from the street when we did go to bed!
Area highlights: Aifur (viking bar/restaurant), Pharmarium (beautiful boutique bar), Stockholm Ghost Walk (cheesy but so much fun), and the Kaffe Koppen (try the 'pies' for breakfast, they are actually quiche).