Kaliningrad used to have seven bridges, only two remain. The problem is could you walk through the city and cross over all seven of them (completely, not half way and then retreating) only once. They were laid out like this.
This problem was first solved by the Swiss Mathmatician Leonhard Euler.Why am I calling it Kaliningrad and not Konigsberg its original name? Well, unlike Leningrad, it is still named after Mikhail Kalinin.
This is despite the fact that Kalinin was one of the most loyal Stalinists. He even allowed is own wife to be arrested and sent to a labor camp. She was thrown naked into a freezing cellar, beaten and forced to change her testimony that she was a rightist spy. (I would never do this to kendra.) Anyway, it is better than naming a city after a king.
