Sirena Beach is a part of Isle Delfino, a beach with warm, golden sunsets, target of electric goop in Super Mario Sunshine, and the home of Hotel Delfino, a unique four-star hotel. The hotel is, in quite a few episodes of the level, being attaked by Boos. The hotel owner allows Mario to enter to hotel at no cost in return for exterminating the Boos.
Sirena Beach is also the level in which the Manta Storm boss is fought.