I will be in Paris this weekend dropping my kids off at summer camp. I’ve been there several times, mostly doing touristy stuff with the family or shopping with friends. Since I only have one real day after dealing with jet lag from Canada, what really cool thing could we do/see that we probably haven’t done before?
Ideas?
I missed it on my last visit there but my wife said the catacombs were very cool.
There are some cool libertine clubs you could hit, but normally you need to be a couple to get in, and the fun normally doesn’t start until about 10:00 pm.
Go up The Eiffel tower. You can see all of Paris and it really is quite an experience. It’s also of course the most obvious thing you could do in Paris with limited time.
This is what I was going to say, though it’s probable the OP has done it already, as part of “doing touristy stuff” on previous visits.
If not, though, I second the suggestion. Yes, it’s completely obvious and touristy, but it really is a very cool experience, and after all, the Eiffel Tower is the very icon of Paris. You can forever say “I’ve been in there!” whenever you see it. 
Other than that, the most fun I had during my short stay in Paris was simply wandering the city as a pedestrian. Just explore, and fall into any cafe or bar that looks interesting.
Enjoy!
That is my suggestion as well. I have been in the Parisian catacombs but relatively few people go so I doubt the OP has. You walk through huge tunnels literally lined with the bones of several million people. The tunnels are huge and they only let a set number of people in at a time so you usually don’t see anyone else around. They are way cool if you don’t get spooked out too easily. I have heard that the sewer tour is good too but I haven’t been on that one.
I did a bike tour of Paris and it was absolutely awesome. There are all sorts of different tours - I did the night time one. 100% recommended.
Go drink chocolate at Angelina’s.
Mmmm…chocolat africain…
<starts drooling like Homer Simpson>
I agree, and I’d also suggest that anyone pay the 5 euro for the audio tour. It adds a lot of interesting stories and stuff.
Thirded. They are absolutely amazing. The sheer number of bones is something to behold in and of itself, but the structures built with them are just incredible. There are memorial markers inscribed with dates the bones were brought to the catacombs, and what cemetery they came from. There are also a few stones here and there inscribed with poems about death. It’s just unlike anything you’ve ever seen, or ever will, and photos simply don’t do it justice.
This are pretty touristy, but we liked it:
You could do a Seine boat cruise.
If you haven’t been to the d’Orsay museum, I’d recommend that as well.
Completely forgot about the catacombs. Excellent idea. Thank you!
Depending how old your children are, Le jardin d’acclimatation is lots of fun – park, zoo, train, small waterpark, playgrounds with somewhat different stuff than the usual over here, some kiddy rides, etc. My son is two, and had a great time. In some parts of the park, peacocks are strutting around uncaged showing off. On the other hand, if your kids are older, they might find it small potatoes.
I’m assuming you’ve been to the Eiffel Tower before, but if you want to get up on a building, go to the Tour Montparnasse. It’s excessively ugly, but the view from the rooftop is spectacular. They’ve recently renovated the rooftop, so you can even sprawl out and have a picnic lunch if it’s a dry sunny day. There’s a glass wall around the entire thing that allows great views in every direction. Less of a wait to go up than the ET, and the best view you’ll ever have of the ET itself.
The Catacombs are indeed very interesting, but I guess again it depends how old your kids are. For some people, it’s a tough climb down into and up out of (though maybe that’s changed – I was last there in 2002).
For my money, Le parc des Buttes de Chaumont (in the 19th) is the most beautiful, interesting park in Paris. And it’s not too far from La Villette, which has a huge sort of interactive science/technologie installation for kids (I assume your kids speak French if they’re going to summer camp in France). You could certainly make a (long) day out of these two places. Les Buttes de Chaumont on a sunny day is heaven to me. Bring wine and cheese and baguette.
I haven’t been in a heck of long time (at least ten years), but the massive flea market just north of Paris at St. Ouen was definitely interesting back when I used to go. Far and away different from what I was used to in NA. And not far north of Montmartre if you want to make a day of the two.
Organ concerts at La Madeleine were often quite thrilling.
I’m not sure if it’s still there, but this summer, they had a fifty metre pool in a boat moored in the Seine just outside the BNF. It looked inviting; I wish we’d gone for a swim in it.
Listen to the concert and tour the organ at San Sulpice.
Usually after the Sunday morning mass so ~11:30-12:05. After the tour, the organist’s wife guides people (gather at the back right side of the church) up into (literally) the organ to see it firsthand. It is unusual but quite an experience. The organist is world renowned and he really lets the organ “jam” for the concert.