Greetings 

I need some advice.  I am currently in Nimes and would like to visit the Chauvet cave.  After a long search I found the only option to get there by public transport.  Ať first tgv to Valence and then ter bus to Vallon pont d'arc.  As I read in other posts here on the forum, railpass should be valid in ter bus, although I'm not sure if it's still true and if the bus driver will know it too.  App shows me that they also need a Seat reservation for this bus. 

1. Do I really need to reserve a seat for this bus?

2. Does anyone know of any other way to get to Chauvet Cave in a different way and earlier, or at least how to leave Vallon Pont d'arc later.  I found the last connection to the train station at 17.00. 

Thank you for your help