Rock Bottom is a small city in a deep-sea trench located beneath Bikini Bottom. It first appears in the episode of the same name and makes other appearances in the franchise afterwards, but does not make its second episode appearance until "Out of the Picture."
The road between the two cities is so perfectly vertical that it can only be accessed by a bus or balloon. It is a 90 degree angle, as confirmed in "Rock Bottom."
Sunlight does not reach this part of the ocean, so everything is always pitch black except for a few street lights. Signs are written in a language based on English, except with the letters distorted, inverted, or in a different orientation. The soil is green with living sludge that can talk. Most residents of Rock Bottom are bioluminescent and generally very creepy looking. They speak a language nearly identical to English, except that they blow raspberries between most words and sentences.
The entry area of Rock Bottom contains a "Kandy" machine. The road leads back to Bikini Bottom and restrooms, although foreigners cannot tell which is the men's room and which is the women's due to the weird symbols used to mark them, and are unable to determine the genders of the inhabitants.
Rock Bottom also has a major bus station, although the bus is extremely hard to catch. There is also an information booth, with extremely long waiting lines. SpongeBob has attempted to be first in line, but the lines are already taken so he is forced to be 329th in line.
There is also a police station and a prison, as seen in the video game SpongeBob's Boating Bash. There are many billboards throughout the town. Lastly, the signs on the bathroom doors have question marks on them.
In Battle for Bikini Bottom, Rock Bottom is the sixth level in the game in order. The main mission of the level is to collect artwork stolen from the Rock Bottom Museum and return them to Mrs. Puff. The player also travels to the Trench of Advanced Darkness, a trench that is lower than the city itself. There is also an episode reference to "Rock Bottom" in the game; if SpongeBob approaches the Kandy Machine, a small cutscene will play and a bus will stop next to the machine before leaving.
In The Yellow Avenger, this is where the player finds the Flying Dutchman. They can also see the bus station, which is accessible. There is also a giant anchor, and a vending machine can be found inside the bus station.
It appears in SpongeBob's Truth Or Square during the 24-hour shift flashback level. It is where the entire level occurs and takes place.
It appears in the game SpongeBob's Boating Bash as a driving area.
"The String"- Rock Bottom was presumably destroyed when SpongeBob unraveled all of Bikini Bottom and the Milky Way with the string.
The outlandishly creepy appearance of Rock Bottom's residents are based on the appearance of deep sea creatures in the real world, which are generally more "deformed-looking" than sea creatures in higher levels of the ocean.
It has an appearance similar to the monster-infested trench on the way to Shell City.
Rock Bottom makes its second in-series appearance in the season 10 episode "Out of the Picture," marking the city's first appearance in the show in 17 years.
If the road is at a 90 degree angle, buses wouldn't be able to get out.