Check out the new high-speed links from Paris to south-west Germany, TGV Est Européen.
From Paris it's three hours to Mannheim (romantic Heidelberg round the corner) or Karlsruhe (Black Forest nearby). Or 4-ish to Frankurt or 6-ish to Munich.
Changing in Paris couldn't be easier (10 minutes by foot) - from the Eurostar terminal at Gare Du Nord, walk round the corner to the magnificently restored Gare De L'Est and hop on your TGV or ICE (= the German TGV) towards Germany.
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