The beaches along the coast south of Orbetello are dotted with lovely establishments with cafes, bars, showers, bathrooms, and umbrella and deckchair hires with parking nearby. But if you really want to get away from that, and everybody else, head for either the long beach across the isthmus at Feneglia, the rocky little coves of Argentario, or the beaches of the Maremma National Park.
The main entrance to the national park is at Alberese, which is sometimes regulated to not let too many cars through at one time, and from where there is a beautiful drive through the park to the wild and untouched beach at Torre di Collelungo, one of the medieval watchtowers along the coast. The beach is dotted with driftwood, offers a beautiful view along the National Park coast back to Argentario, and is untroubled by any facilities or amenities at all, so take everything you need with you. It’s gorgeous.