Since it's 100 years since WW1, it might be worth visiting the front line.
Start in Ypres (Belgium  ), continue to Verdun (France  ), and cruise in the Vosges (also France). Go down to Swiss (stay of the highways if you don't want to buy a vignet), ride the Apls to France and cruidse back to Calais.
... and hope for sunny weather ...
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