This Roman Arena is almost 2000 years old. In spite of this, it is in great shape. In fact, the arena is still used for events -- mainly bullfights.
We were at the Colloseum in Rome last year, and this one is in better condition, though they have made some modifications to it for present day use. Its quite incredible that they are able to both preserve and use this historical building. Once inside, you are free to walk almost anywhere. We climbed to the top of one of the towers for a good view of the town and the Rhone River.
This arena is included on the Monument Pass (we bought our pass at the ticket booth here).