there are twelve hundred bridges on the canals , all in the shade of magnificent avenues of elm trees ... '' they passed the smalste huis - the narrowest house in amsterdam - which was only as wide as the front door , and the westerkerk with the crown of the hapsburg emperor maximilian , and they went under the wooden lift bridge over the amstel and the magere brug - the skinny bridge - and passed scores of houseboats that served as home for hundreds of families .