On a clear day, it is possible to see the opposite coastline of England from France and vice versa, with the most famous and obvious sight being the white cliffs of Dover over 20 miles from the French coastline and shoreline buildings on both coastlines with the naked eye, as well as lights on either coastline at night, as in Matthew Arnold's poem "Dover Beach".
http://en.wikipedia.org/wiki/Strait_of_Dover
