The streets in Freiburg all had these drains running down the sides with fast flowing water keeping them clear. Very cool, added an extra dimension to every street.
From Wikipedia: The city has an unusual system of gutters (called Bächle) that run throughout its centre. These Bächle, once used to provide water to fight fires and feed livestock, are constantly flowing with water diverted from the Dreisam. These Bächle were never used for sewage, as such usage could lead to harsh penalties, even in the Middle Ages. During the summer, the running water provides natural cooling of the air, and offers a pleasant, gurgling sound. It is said that if you step in a Bächle, you will marry a Freiburger, or 'Bobbele'.