Amsterdam: narrowest house in the city

First day in Amsterdam: took a walking tour and was shown this little house. The story behind the house (as we were told): a man saw an extravagant building nearby with many windows and told the architect that one could survive in a house just the width of one window -and the architect built this house as a response! I wonder how the owner gets upstairs -by a super steep staircase or by shimmying up a rope? x