evidence: Lake Constance is the third largest lake in Central Europe, and sits at the point where Austria, Switzerland, and Germany intersect. It’s a scenic bulge in the Rhine River popular with tourists for its castles, boating, bike trails, and Alpine scenery. Locals call it by the old German name, "Bodensee," but in most other European languages, it’s named for the city of Konstanz, on its western shore. On land, the borders between the three nations are well-demarcated. Since 2007, for example, the border between Switzerland and Germany has been marked not by a fence, but by a work of art: 22 giant statues by Johannes Dörflinger representing the cards in a tarot deck. But in the water, everything changes. Look at Lake Geneva on a map and you’ll see that the French-Swiss border passes clearly through the lake. But on a map of Lake Constance, the international borders just end at the waterline. There’s never been a treaty demarcating the border, so Lake Constance remains a borderless black hole in the middle of Europe!