We took the coach from Cagliari to Villasimius and it took 1.5 hrs (I think it was 6.50 return per person). When we got off at Villasimius (the street is called via Roma) we walked down to the centre.If you are confused where to take the shuttle to the beach from,you will come to a square on via Umberto I. The shuttle runs every hour and it's 2 euros one way. You reach Simius by walking (20 mins) from the here at the square or you can get the shuttle.The shuttle goes to 2 other beaches and then to Porto Giunco.
The sand at Porto Giunco was so soft.The water crystal clear.It was packed with people but we loved it anyway.