Friday Night Fever
If you're ever in Paris on a Friday night, head down to the Montparnasse area for Friday Night Fever, the nighttime rollerblading tour of the City of Lights. Thousands of skaters get together for this once-a-week event (weather permitting).
If you don't have your skates with you, you can grab a table at one of the cafe-bars at the intersection of Boulevard de Montparnasse and Rue de Rennes, order a drink, and watch the crowd go by (it takes about 5 - 10 minutes). It's quite a sight!