It’s always easier to visit a place with a pass and I think you should get a Museum Pass when you visit Nimes for a day. All of the tourist attractions in Nimes that I have been to are within walking distance. Therefore you don’t really need to worry about the transport, all you need to get is just one single Museum Pass and that’s it. This literally made my life a lot easier. Haha!
One pass includes the entrances to three places: Arena of Nimes, Maison Carree and La Tour Magne. And of course, it saves you some money when you buy a pass instead of paying the entry fees separately. I like the Arena of Nimes most because I did not only see the most well-preserved Arena in the world, but also some nice views from inside. You will also be able to see the Nimes as a whole from far and the top when you climb up to the La Tour Magne. I was climbing up so many stair for the view that I was dying for but the view of Nimes from far and top wasn't really overwhelming to me...
And Maison Carree was totally something that I did not except it was... I thought it would be a history museum, or somewhere that I could actually walk around inside to have a look of the architecture or so. However, it's only a theatre inside with a timed schedule of playing a short movie about Roman history of Nimes... The movie was great and I did learn something from it. It's just something that I expect to see though... LOL
If you are not interested in their ancient history, perhaps you don't even need the museum pass...