Are we crazy to want to rent a car (perhaps from Orly?) and drive down to Lascaux from Paris? We see there's a tour of more than one cave site out of Sarlat that looks very interesting. We're in Paris for a month, and thought a three-day break would be nice.
What's crazy about it?
Mind you I'd want to spend a bit more time there especially after such a long drive (1 day to, 1 day back, and only 1 day there). And I don't get the Orly thing.
It's a lovely region.
Orly would be a good place to rent a car you're taking south from Paris. But you might look for other places on that side of the city, reachable by Metro but far out enough not to get too much traffic. We rented from Hertz on Avenue du Maine near Gare Montparnasse, it was a little more traffic than I liked but not too bad. Porte Maillot, on the Peripherique west of the Arc de Triomphe, would be another good jump-off point.
I'm sure you know that "Lascaux" is actually Lascaux II, a recent reproduction of parts of the actual cave. We thought it was very well done, with a good English-language tour. They replicated the contours of the actual stone so you can see how the animal paintings were designed around the shapes the painters found. And they used dyes from the same plants the original painters used. Well, I mean the same plant species....;) Also the lighting is better, enabling you to see the art better, because they don't have to minimize it to protect the paintings. All in all, we thought, a worthwhile experience even though not "the genuine artlcle."
Not far away is Font-de-Gaume, an original cave with limited entry (as I think is the case with all the other major caves). Pech-Merle, which I haven't seen but which many people rave about, is further south. I'd suggest more than one full day in the Dordogne to make the drive worthwhile, maybe give it two full days and three nights. With a month in Paris you have time for side-trips like that (lucky you!).
I think all the caves require either advance-purchase tickets or showing up very early to get in. The RS guidebook and other good ones have more information.
So, short answer, you're not crazy. At least, not for wanting to make this trip!
We have spent time in this area several times and love it. Lascaux II is definitely worth seeing, but the Font du Gaume is the gem -- the real deal. There is very limited access and I would strive to reserve ahead (use the french site, the English one doesn't offer reservations) Peche Merle is a beautiful cave but the cave art with the exception of the one famous piece 'the spotted horses' is unimpressive.
Try to also do a canoe trip on the Dordogne (not the Vezerre which is boring in comparison). The stretch above Le Roque Gageac is gorgoues and you can get a service that will run you up river as far as you want to go -- we did a leisurely full day paddle, but you can do shorter runs.
When you visit Lascaux try to get dinner in Montignac at the Hotel Roseraie We have stayed there (nice provincial hotel) and have eaten dinner there several times on trips through the region. We have always had a beautifully presented elegant dinner at prices a third that of a similar experience in Paris.
Those caves around Sarlat, both original and reproduced, are among the most special sites in Europe, in my opinion. Trains from Paris to Sarlat take 6 hours each way, with a connection at Libourne, or Libourne train station could also be a place to pick up a car (closed Sundays and lunchtime).
Rick’s France rail travel page has the link and tips for buying “Prems” rate TGV tickets through SNCF (cheap, reserved, nonrefundable, available three or four months ahead of your travel date) to print at home and pay with PayPal. It does not tend to work with US credit cards, unless you have an extra level of security set up.