This is a map of old-time Kongsberg. The green shapes are bridges which connect the different parts of the city. Can you find a path through the city which goes through every bridge exactly once?
No, you can't. Notice that if you enter and leave some part of the city, the number of bridges you go through increases with 2. Therefore there can be at most 2 city parts which are connected with even number of bridges with the rest of the city. However, on the map you can see that there are three of them, which implies that the task is impossible.