This is a bridge in Paris. You hang locks on it with the name of you & your boyfriend/girlfriend/best-friend then throw the key into the river. so even though the friend/relationship may end, you can’t remove the lock. It stays there forever, as relevance to someone once a part of your life.
Oh! This explains it! I saw the same thing in Cinque Terre, in northwestern Italy — on the Via Dell’Amore, which is just what you think it is.