Rock Bottom is a city located within a deep trench that lies below Bikini Bottom. Rock Bottom first appears in the episode of the same name. While making appearances in video games, it doesn't appear in the show itself until the season ten episode "Out of the Picture."
The city is only accessible from Bikini Bottom from a road that drops at a perfect straight line, as when SpongeBob attempts to escape, he is unable to after recalling his grandfather's quote about 90° angles. Since sunlight cannot reach Rock Bottom, it's citizens also appear distinctly different from the citizens of Bikini Bottom. Many citizens of Rock Bottom are bio-luminescent. The city also has a differing alphabet and dialect from Bikini Bottom as well. In Battle for Bikini Bottom it is revealed Rock Bottom has a renown art museum and that Barnacle Boy works there as a part-time security guard. The bus stations in Rock Bottom are also very unpredictable and unreliable as shown in "Rock Bottom."