This public beach in Portofino is located in Cannone Bay, right at the entrance of the town. It's quite small and likely in the summer it gets packed, but I visited in April and even though it was a warm day, there were only a handful of people enjoying the sun.
The beach is rocky, and the water looks incredible! Surely, the perfect place for a swim if you are in Portofino in the summer. There are larger beaches nearby, but they are not technically in Portofino though.