Well worth every penny - Incredible trip through geological history. Stalagmites and stalactites galore ,tight squeezes and then huge open chambers. Loved it.

Pleasant day trip out of Lyon - About an hour north of Lyon, the caves were a pleasant surprise. Our teen enjoyed it as much as we did. Absolutely massive, full of all kinds of cool formations, with lots of steps at the end (most of which can be skipped - there is a warning sign). At the entrance, there are 3 parking lots, a shop/cafe, and restrooms. There is also WiFi for downloading the app (obviously, no reception once you're down below) - the app does a decent job of explaining formations and cave history, but the audio didn't work for me in the cave, only the text descriptions did. I did see some people listening to the audio, though, so perhaps, you need to pre-load the entire thing before descending. The walking path doesn't require any special footwear, though non-slip soles are recommended. Cool, steady temperature year round, making it a great activity in any weather.

A bit of a hidden gem - We found the Grottes du Cerdon on a list of things to do within driving distance of Lyon and combined it with a stop in the medieval town of Perouges. As did the previous reviewer, we downloaded the audio tour, but also were unable to access it once we were in the caves. I think there was a local wifi that might have been accessible in the cave (that’s the only thing I can think of that would have allowed access to the audio tour, other than physically downloading the podcast to the device). I do recall seeing a sign for the local wifi in the ticket office. The audio tour webpages did contain text so we were able to read what we assumed was the script of the audio tour. I think we were as impressed with the caves as the previous poster. Some areas were fairly narrow, but the middle portion was massive. It was cool in the caves (I think they said somewhere it was only 4C) and while we were fine in shorts and t-shirt, I would have brought along a sweatshirt if I had been prepared. The length of the cave system is about 800 metres, and the elevation change is about 40 storeys, but it was not an especially challenging walk.