Sirena Beach

Sirena Beach is a part of Isle Delfino, a beach which is the target of electric Goop in Super Mario Sunshine, and the home of Hotel Delfino, a unique four-star hotel. Mario only visits the place in evenings. It includes a snack bar, 2 pools (one in the form of a sauna), and a Casino. The hotel is, in quite a few episodes of the level, being attacked by Boos. The hotel owner allows Mario to enter to hotel at no cost in return for exterminating the Boos and defeating Phantamanta.

Sirena Beach is also the level in which the Phantamanta boss is fought. Mario also fights King Boo here in the Casino. Peach, Toadsworth, and the Toads were probably meant to stay here, but because of the crisis, their stay was cancelled.

Once Mario enters the Casino he can't go back into the main lobby. And he also can't get back outside once he goes in the hotel. The pipe that leads to Sirena Beach is covered by a pineapple that only Yoshi can eat. The pipe is red.

Episodes
Episode 1: The Manta Storm

Hotel Delfino has been completely covered by electric goop and has sunk into the earth. Mario needs to fully defeat the Phantamanta in order to receive the Shine Sprite. Once Phantamanta is defeated, Hotel Delfino is restored.

Episode 2: The Hotel Lobby's Secret

The hotel is back, but the lobby is filled with Boos. Mario needs to use the Pink Boos in order to reach the top of the totem pole which has a golden statue of a Boo. Mario will have to jump into it in order to go to a secret level with the Shine Sprite.

Episode 3: Mysterious Hotel Delfino

The hotel is operating. Mario needs to use Yoshi in order to access the pool room from the attic to get to the Shine Sprite.

Episode 4: The Secret of Casino Delfino

The hotel is now open. Mario needs to find a way to get triple 7's on the big slots and solve the Shine Sprite puzzle. After solving the puzzle, the player wll end up in a secret level.

Episode 5: King Boo Down Below

The casino has closed down. Mario has to defeat King Boo by the use of Chili Peppers, water, and fruit.

Episode 6: Scrubbing Sirena Beach

The goop has returned, and Mario needs to clean the entire beach in under three minutes.

Episode 7: Shadow Mario Checks In

Another Shadow Mario appearance. This time, some of the Boos will look like copies of Shadow Mario.

Episode 8: Red Coins in the Hotel

Mario needs to track down 8 Red Coins in various places in the hotel.

Trivia

 * Sirena is "Mermaid" in Italian so the translation would be "Mermaid Beach".
 * It may also be noted that "Sirena" is similar to "Serene." The Sirena Beach is indeed a serene place.
 * In Super Smash Bros. Brawl, the pipe to the beach is absent in the Delfino Plaza course.
 * The goop in episode 6 is arranged into a smiling boo shape.
 * The music in the hotels casino is similar to the music when playing Luigi's minigames on Super Mario 64 DS and New Super Mario Bros.