Paris is a place that both my parents and I have been very fortunate to visit before, and so our time there mostly included soaking up ambiance and enjoying the beautiful city (ok, and a trip to the embassy for me- always more Peace Corps paperwork to do)
I find France's relationship with WW2 to be very interesting, especially given that I now live in a part that was part of the Vichy government. Aside from that, I also find the different plaques and monuments interesting as well. While it's not exactly a jolly adventure, we did go by the Shoah memorial, not far from Notre Dame.
There were also happier aspects of Paris, like the locks that weight down bridges, which are meant to signify two people in a relationship locked together (you throw the key in the river), so if you change your mind later, you better get swimming or bring a lock cutter.
Of course, Notre Dame. Though they are doing this "pilgrimage year" thing, but it includes a large stand in front of Notre Dame in the square, which means it's difficult take any good pictures anymore. Whomp.
At the Pantheon which includes the final resting place of important figures like Victor Hugo and Marie Curie.
It's not quite secular or religious, but the Pantheon is meant to represent France and the city of Paris. A temple for the city.
I watched "An American in Paris" while we were there, so I couldn't help but take photos like this while we were there. It's got some scummy sides too, but Paris really is a beautiful city.
Not a bad place to spend a few days with Mom and Dad :)