In his Amazing Places series, Tom Scott pays a visit to Lake Constance, a body of water that sits between the borders of Germany, Austria, and Switzerland. While Lake Constance is considered to be a shared property of the three countries, they can’t quite agree on exactly how it’s shared because there is not a binding agreement about where the borders fall on the lake itself.

If you’re sitting on a boat in Lake Constance, are you in three countries at once? Or just in one? Does it even matter? Because strangely, it turns out there are parts of the world where no-one really minds when international borders are not just ignored, but are completely undefined.