There were a few other places we visited briefly including Cologne, long enough to tour the famed cathedral. The rain combined with traffic made it so we pretty much had to turn around without doing much of anything else.
We also spent a few hours in Luxembourg viewing the old casemates and battlements, watching the gurard in front of the Grand Palace, and eating a delicious lunch. We also stopped at the nearby US military cemetery where General Patton is buried along with over 5000 soldiers (most killed during WWII; the Battle of Ardennes and liberation of Luxembourg.)
We took advantage of a few hours of afternoon sun to take a hike to Devil's Gorge near the German village of Irrel and were rewarded with some pretty spectacular scenery.