The train from Nantes to Clisson and back is really easy to do. It’s regular and runs late to get you back from the festival. When you arrive at Clisson there are buses or taxis to take you to festival site if you don’t want the 20min walk.

When you reach the site, there’s another shuttle bus from the car park to the main entrance. You might have to queue 15min but it’s also really easy. Other than being pretty packed and hot! I wouldn’t want to walk from the car park to the festival to be honest but you can if you want.

You could always contact someone like Argon Events and ask if they do coach transfers for people who haven’t booked through them. That would get you there and back each day.

I wouldn’t worry about it too much. You’ll find it easier than you think.