Hotel Delfino
The Hotel Delfino is a luxurious hotel located in Sirena Beach, the sixth world of Super Mario Sunshine. The hotel is run by an extremely wealthy Pianta. Outside the hotel it's always evening. Inside is a maze of rooms, air vents, and a large casino. The Pink Boos make their first appearance here.
At first it completely disappeared under electrified goop after Phantamanta stormed all over the place. Mario defeated Phanta and the hotel came back. Then when it rose up the place was covered with Boos. Though the Boo activity slowed down after King Boo was beaten by Mario there still were some Boos still hanging around. In Shadow Mario's level, all the doors are unlocked, making it easy to explore the area and collect Blue Coins.
Casino
The casino is a sub-level of Hotel Delfino (which is itself a sub-level of Sirena Beach) in Super Mario Sunshine. Here Mario has to fight King Boo. It also includes two jumbo slot machines in which Mario can win coins or produce a Boo by spraying it with water. There are other slot machines that Mario can ground pound to get more coins. There is also a tile set Mario needs to match in order to access a secret stage. A roulette wheel is in the center and in the fifth mission, Mario has to Ground Pound a special purple tile to reach fight King Boo. Once Mario enters this area, he can't leave. He can only enter the casino in episodes 4 and 5.
Music
The music of Hotel Delfino features rhythm ukulele, electric bass, and various percussion instruments, including bongos, congas, güiro, marimba, vibraphone and wooden wind chimes throughout. A theremin-like synthesizer comes in and out with the melody. The casino's music is completely different; rather, it implements saxophone, honky-tonk, piano, electronic organ, upright bass (pizzicato), whistling, and a drum set.
