Cerulean Beach is a location in Mother 3 west of Tazmily Village. Bateau and Dona's houses are both here, and Nana can frequently be seen looking out at the water. The only way Lucas and co. can get from the main area of the Nowhere Islands to Tanetane Island in Chapter 7 is by walking from here along the sea floor. Dolphin Ossicles can be found along the beach shore.
Before becoming more modernized in Chapter 4, there is an Edible Mushroom in a gift box. After Flint gets the Drago Fang from Bronson, both Lighter and Fuel can be found here; Lighter is down in the dumps at the thought of Flint flying into a rage in front of his kids like that and how it can negatively influence them; he also adds that Claus is probably going to try and avenge Hinawa's death so he lends Flint the Manly Bandana. Jonel, Bud, and Lou can also be found at various times.
From Chapter 4 onwards, Bronson and a pig can be found sunbathing (and Bronson will let the party relax there, restoring their HP and PP), and a Save Frog in a barrel appears on the beach. A vendor appears and will sell Aloha Coats, Giant Abalone Steaks, and Jumbo Shrimp Soups. Benches for lovers (and lovers themselves) appear on the beach's westernmost area, and Bob can be found in Dona's house. A woman with the sprite of Mysterious Lady will appear on a bench to the west and will, after responding yes, take Leo's Sweater. There is no point in this, just for a line of dialogue.