We have loved this quirky apartment and were fine with the stairs- the two bedrooms we had access to were spacious, one with the little balcony with a great view of the square, the other very much ‘under the eaves’ and not for tall folk. As others have mentioned, the tiny ‘kitchen sink’ area is tricky for more than a couple of days, tho’ there is a microwave and toaster which we didn’t use, and the fridge works well but no freezer section for ice. We felt the view and historical aspects of the building made up for the minor defects, and the position is perfect for exploring everywhere, but for a big group having one little shower in the laundry might be an issue.
Fredrik has many plants and objets d’art around the place and has renovated this unusual place very sensitively- we’d highly recommend it for a short stay in beautiful Stockholm!
Also recommend getting a public ferry out to at least one island in the archipelago- we went to Vaxholmen, a gorgeous, inexpensive trip and ferries go hourly- gives a great idea of the less touristy Stockholm.