The Treehouse in Columbia City, Seattle, was a great experience. Lovely place! We were four of us, two adults and two kids, and the apartment was big enough and has great atmosphere + everything you need. The lovely weather meant that we spent a lot of time on the veranda, playing cards :-)
Columbia City is a nice neighborhood, and we would recommend that everyone tries the brunch at Geraldine's Counter.
Jay and his wife are great hosts, very friendly, quiet, and welcoming. I greatly recommend the place.