There's the Rhine. And notice the sky... lots of trails left by planes coming and going from Frankfurt. It was in the vicinity of Frankfurt airport (each time we passed through) that we had our closest encounters with other planes. Unfortunately, I was too slow on the trigger to snap them. It's fairly hair-raising to have another plane cross your path, either directly above or below, at such a great rate of knots that it's gone before you can even click a camera at it ! No doubt they were flying at regulation altitudes, but they seemed so darned close !