The [Sun Thalys](http://www.nshispeed.nl/en/travel-with-thalys/travelling-with-thalys-to-southern-france) runs during summer and connects Amsterdam (close to the North Sea) with Marseille at the Mediterranean ocean. It only runs during summer and I think it was claimed to be the longest distance direct high-speed line in the world at the time (EDIT this may have been true in 2012 but no longer, as there are now longer services in China). It more or less crosses Europe from coast to coast.