Sardinia

While we stayed in the main part of Bosa, a mile and a half inland, a beachside community has developed right where the Temo River enters the sea. In April two years ago, there were serious-looking waves.

Elsewhere, we didn’t go southeast of the capital city Cagliari, but I understand there are popular beach towns in that direction.

I always stay at Santa Teresa di Gallura, but always had a car. There is a beach in town too.
San Teodoro has LaCinta beach walking distance. However I recommend renting a car to see more. Castelsardo is nice, but not sure if there are nice beach within walking distance.

We enjoyed Santa Teresa di Gallura as well, and it's also very convenient for getting boats to the Maddalena Islands, which have some of the best beaches in the Mediterranean. I agree it's a lot easier to stay there if you have your own car (I'm not sure how you'd get there on public transport from any of the Sardinia airports).