While jellyfishing in Jellyfish Fields, SpongeBob and Patrick encounter an object sticking out of the ground. They decided to dig it up, and they discover an old submarine. Meanwhile, at the Krusty Krab, Squidward and Mr. Krabs think of an idea, to bring the Krusty Krab to the customers. SpongeBob and Patrick drive the submarine into the Krusty Krab, which makes Mr. Krabs have SpongeBob and Patrick take the submarine and sell Krabby Patties. Seeing this, Plankton gets upset since he had the idea years ago. He takes the fist of the Chum Bucket and uses it as a mobile Chum Bucket.
SpongeBob and Patrick are unsuccessful with their first customers, so they offer to pay them. Meanwhile, Plankton attempts to sell food to a child, which he insults. The child's parents, great grandmother, Harold, and Jack M. Crazyfish throw rocks at him. Soon, they run out of rocks, but since Patrick wasn't paying attention to the Krabby Patties, they have turned to rocks. SpongeBob and Patrick are able to sell the rock patties, and then head off to sell more.
They fell into an abyss and woke up a sea monster, who has been asleep for the past 79 years. The monster purchases 640 Krabby Patties. Plankton comes along, and attempts to get the monster to refuse the Krabby Patties, but Plankton is mistaken for a dessert (a chocolate éclair) and the monster chases him away. Because they are down in the abyss, SpongeBob and Patrick have to let go of all the money they have earned. Instead they bring back 37,000 pounds of decorative undersea rocks, much to Mr. Krabs' disappointment.
Home video releases
- SpongeBob SquarePants: Pest of the West
- SpongeBob SquarePants: Season 5, Volume 2
- SpongeBob SquarePants: The First 100 Episodes
- SpongeBob SquarePants: The Complete 5th Season
- The sea monster is voiced by Gene Simmons who is well known for being the bass player for the band KISS.
- The mother who is insulted by Plankton is voiced by Simmons' partner Shannon Tweed.
- This episode reaired with "Krabby Road" when the latter premiered.
- This episode was set to premiere with "SpongeHenge" but aired with "The Battle of Bikini Bottom " instead.
- Mable's grandson was shown as the truck driver in "The Gift of Gum" and "Slide Whistle Stooges" In this episode, he also has his trucker's outfit.
- In the English version, the monster said he didn't eat for 79 years, but in the Netherlands he said 97 years.
- The salesman from Chocolate with Nuts returns in this episode, and cons SpongeBob and Patrick one more time, this time without even trying, as they hand him money for trying some Krabby Patties, it seems like he remembers SpongeBob and Patrick, as he says "Hey, thanks AGAIN guys." He is also shown to be married.
- Running gag: SpongeBob drives the submarine and bumps into the Krusty Krab, destroying the window.
- Jack M. Crazyfish, who appeared in Blackened Sponge, can be seen hurling things at Plankton.
- It is revealed that Plankton's fist on top of the Chum Bucket is actually a submarine.
- It is shown again in this episode that scallops can be tamed and used as pets.
- In a way, SpongeBob and Patrick helped The Chum Bucket more than the Krusty Krab because the monster preferred Plankton's chum over the Krabby patties.
- The monster is the only creature so far that actually likes Plankton's chum, because all the fish in Bikini Bottom refuse to eat it or throw up when they do. Nat seemed to like it, but was only pretending because Karen was paying him to eat it and it actually made him sick.
- Though, Patrick is also seen to like Plankton's chum.
- The sea monster breaks the fourth wall. After thinking Plankton was a chocolate eclar, he looks at the screen saying "Now that looks like dessert to me."
- The title is a spoof of Jules Verne's classic novel, "20,000 Leagues Under The Sea."
- It was a short distance between the grass in Jellyfish Fields to the submarine stuck in the ground but later the grass isn't seen.
- When the sea monster takes submarine off his head, the periscope at the top of the submarine is missing.
- It is unknown how the Sea Monster knows that he has slept for 79 years.
- Plankton's mouth wasn't syncing with what he was saying when he said "Ah, who needs that old rust bucket anyhow."
- At one point, the lenses of SpongeBob's glasses are the wrong shape.