Sveti Ivan, just one bay north of the Blue Grotto.
The legendary blue of the Adriatic Sea - this is where it belongs. The only way to enter the cave is by swimming.
If you don’t feel like walking down to the beach (it’s a challenging hike! Don’t forget to bring food and water - there are no facilities there), rent a boat and take the water route.
Just south (i.e., one bay over) from one of Croatia’s most beautiful beaches, Sveti Ivan (which is accessible only on foot or by boat), lies the Plava Grotta, the famous Blue Grotto of Cres.