We had an absolutely wonderful stay at William's place. It's located only footsteps from the subway station in the Gamla Stan of Stockholm, only steps from the Royal Palace, as well as the tourist-trap street next door that can't be missed.
Notwithstanding its super-central location, the apartment is quiet. Once you climb the somewhat tiring stairs (par for the course in this neighborhood), you are treated to a wonderfully outfitted top-floor apartment with sloping ceilings and lots of nooks and crannies. It's set up for people sleeping in two areas far from each other so you can travel with people you might not like enough to share a bedroom with and stay here.
Communications with William and his co-hosts were excellent. One of us had a flight delay, but the hosts were accommodating and met up with us when we arrived, even though it was several hours late. Questions we had about the apartment were answered in seconds or minutes at worst!
Couldn't be happier.