Arnensee Lake, Switzerland
The waters of Arnensee in Switzerland are so clear they cause boats such as the one in the picture to appear as they are hovering in the air.
The lake is located in Canton of Berne in Switzerland, and can be easily reached with a little planning. Although that first picture has made the lake relatively known, it’s still usually a quiet, tourist-free place.
Lake Geneva gets like this sometimes, too, though mostly in winter.