No visitor should miss out on a canal tour of the splendid canals of Amsterdam. The canals, which were declared a UNESCO monument in 2010, aren't just a picturesque attraction, but were essential to defense and transport in 17th-century Amsterdam. With the arrival of the automobile, hundreds of canals were filled in nationwide to accommodate the new mode of transport, but Amsterdam has retained 165 of its historic canals, more than any other Dutch city.