Poking around in my photos database, I came across two more pictures like yesterday's. I just read on Wikipédia.fr that there are approximately 25,000 habitations trolodytiques in France. There are even villages troglodytiques in many French regions, including the Loire Valley.
Troglodyte houses can be fairly elaborate, like the two in my photos below. The one on the left is in Bourré. The one on the right with the satellite dish is in Amboise. I've only been inside one such house, in Vouvray. It wasn't beautiful inside, but it looked like it was fairly comfortable.