The Cathedral at Reims is an easy day trip from both Paris and Leuven, which is fortunate if you happen to be taking a Flemish Art History class. The cathedral, simply put, will take your breath away. It was built after the fall of the Roman Empire and, until Napoleon, served as the site for the coronation of the French monarch. The Germans destroyed the structure during the First World War, but it was rebuilt following the Armistice.
The Cathedral at Reims:
The building is huge. I was at least 100 yards away and still could barely capture the entire facade.