Pont des Arts: FREE. 1st metal bridge created during Napoléonic reign. Padlocks added to railing w/ names on them and keys thrown into river below to signify commitment to each other (watch for police patrolling to keep people from throwing keys into river).
"For decades now a custom has slowly been creeping across the world whereby loving, romantic, and sometimes superstitious couples have decided to write messages on padlocks, attach them to certain landmarks in specific areas - more often than not railings and fences - and then throw away the key. The practice, as well as symbolising a couple’s unending love for each other, is in some countries thought to bring good luck to a relationship."