Aachen, just across the border from Holland, used to be the capital city of the Holy Roman Empire when it was ruled over by its first emperor, Charlemagne. The French know it as Aix la Chapelle (under which name it featured in the poem "How they brought the good news from Aix to Ghent"). Today it is a bustling industrial city, as unattractive as all such places are, but the centre of the old city still retains a cluster of ancient buildings.
The Dom or Cathedral in particular is well worth a visit, with its wonderful Byzantine-style mosaics, the gold glowing out of the darkness in the flickering light of votive candles. The staff are friendly and helpful (though the website address he gave wasn't as much use as I had hoped, as it is all in German.
When you visit Aachen, keep an eye out for the gingerbread shops which dot the area. They will have you positively drooling, but be warned: unless your teeth are in good condition you'll probably break them trying to eat it!
The second film about Aachen reminds us that it was the first German city to be captured by the Allies in the Second World War.