Google's New Vacation App Was 280 Years In the Making

Kalingrad is a Russian seaport named for a Soviet revolutionary. It sits near the Baltic Sea, between Poland and Lithuania, and it's a place where pre-Putin Russian leaders would occasionally threaten to install nuclear missiles. But in the 18th century, it was a city called Königsberg in the German kingdom of Prussia. And it was a math problem. Königsberg stretched across both banks of the river Pregel, and it included two islands in the middle of the river.