Camargue horses

You might not see the horses playing in the marshes, but renting a car and driving through the Camargue is easy enough to do. Meandering down the roads, you'll easily view the tricolor of the camargue: white horses, black bulls and pink flamingos. Even if the horses aren't playing, it's a unique area and worth a visit. There seems to be more activity in the early morning before the day warms up.

Since you'll be there a few days, speak to some of the locals and most likely they could give valuable guidance.

We had a rental car and just looked for fenced-in pasture and horses. Got nice photos, especially if you come armed with apples and carrots.
The horses are kept in during extremely hot weather and go to the barns at night.
You can Google the roads going through the pastures and plot a route.
We were there in late July, and the mosquitoes were fierce.
But if you want to take professional photos, you'd do better to pay for a tour.

I was a tad underwhelmed by my few hours drive in the Carmague two weeks ago. I saw zero horses. Stopped by the visitor's center in the RS book and she showed me places I might find them that would require 45 to 60 minutes of driving. To be fair, we drove through briefly on our way to Arles so I might not be the best person to answer this.

She also said there were some ponies near the nature center, but we couldn't find them. Not so much on the bulls either. I did see a few huddled together laying down but thought they were cows as they were so far away until the Nature Center lady told me. DID seem some flamingos swimming in the ocean, which was neat, although they were white which I wasn't expecting and I probably would've mistaken them for swans if I hadn't know what I was looking for.

If you're set on great photos, the tour might be worth the money as they can take you to the animals!

At Aigues-Mortes there were many at various places outside the city walls. At Saintes -Maries-de-la Mer many were visible from a boat trip I took. And as mentioned above, you want a super strong mosquito repellent.