If you want a traditional dining experience, you should really have a meal at a Bouillon Brasserie!
I've always been a fan of Chartier - https://www.bouillon-chartier.com/en/ - Great food, unbelievably cheap (still only 1 Euro for Soup of the Day), and a beautiful belle epoch setting. You do have to queue to get in as there are no reservations but it is absolutely worth the wait.
Sacre Coeur is worth a visit
I was going to recommend this. Even if churches are not your thing, the view from there is lovely. You also go through Montmartre to get there which is fascinating.
I was going to recommend this. Even if churches are not your thing, the view from there is lovely. You also go through Montmartre to get there which is fascinating.