Arles has one of the most exciting spectator sports in the south of France, bull fighting. As the city stands at the crossroads between many cultures, there are two popular types, the Spanish and the Provençal. Fights are usually held in the old Roman amphitheater between April and October. The Events & Festivals page has more information for key festivals in Arles that feature bull fighting.
Besides bull fighting, tourists can partake in much more leisurely and less violent activities. First of all, Arles is a city that is easily navigable on foot or by bicycle, so get a map from the Tourism Office in town and walk one of the trails, or rent a bicycle and explore the area around Arles that way. There are also ferries and boat cruises that travel on the Rhône, which provide a nice way of seeing some of the Provençal countryside. There are even places where you can rent horses for a more unique method of sightseeing.
The area around Arles is home to several natural parks and reserves open to the public. In these places, you will find many species of local flor and fauna. There are sometimes guided tours available as well. There are the Domaine de la Palissade (Salin de Giraud), Les Marais du Vigueirat (Mas-Thibert), La Capelière, and Le Parc Ornithologique de Pont de Gau.