So far Rena Majore is one of my favourite beaches in Northern Sardinia. It's a long beach with shallow and very turquoise water.
You have a lovely view on the open sea and the horizon. There's several beaches next to each other. We always go to the one closest to Santa Theresa. The more left one is more crowded but also very nice.
On the very right side of the beach there is a rocky shore great for snorkelling. We found 2 octopuses there.
Sometimes the dunes behind the beach are a bit dirty.