What is the name of the underwater city where the show is set?

The underwater city where the show is set is Bikini Bottom.

Bikini Bottom is the fictional undersea community that serves as the main setting of SpongeBob SquarePants. It is home to SpongeBob’s pineapple, Patrick Star’s rock, Squidward’s moai-shaped house, and the Krusty Krab. Although the characters live beneath the ocean, the city is depicted with familiar surface-world institutions such as restaurants, schools, shopping centers, highways, and cinemas.

The city’s name is a reference to Bikini Atoll, a real Pacific atoll associated with nuclear-weapons testing. The series turns that name into a colorful cartoon setting populated mostly by anthropomorphic sea creatures. Common mix-ups include Atlantis, which appears in SpongeBob stories as a separate legendary location, and Pacific City, which is not the show’s standard setting. Bikini Bottom is also the broader home of locations such as Goo Lagoon, Jellyfish Fields, and Sandy Cheeks’s Treedome.