Pont des Arts Love Locks pedestrian bridge in Paris, walking distance from the Louvre. Write you and your loves name on the lock and throw the key in the river. Would love to do this some day when I go to Paris!
Paris's Lover's Bridge - Legend says that if you and your lover attach a padlock to this bridge, your love will last as long as it stays on the bridge. Each person gets a key to the lock, you decide whether to keep the key or throw it in the River Seine.