From Wikipedia:
"The Parking Garage" is the twenty-third episode of the situation comedy Seinfeld. The episode was the sixth episode of the show's third season. It aired on October 30, 1991 on National Broadcasting Company (NBC).
The episode was written by Larry David and was directed by Tom Cherones, and takes place entirely in a parking garage. The episode "The Parking Garage" has received overwhelmingly positive reviews with many critics calling it better than the previous episode "about nothing', "The Chinese Restaurant".
Plot
The cast is in search of Kramer's car in the multi-level parking garage of a shopping mall after Kramer purchases an air conditioner. Unfortunately, no one can remember where the car was parked. After carrying the air conditioner for some time, an exhausted Kramer decides to leave it behind one of the parked cars and tries to memorize the number of the parking space. Elaine fears that her new goldfish will die in the airtight bag before they can arrive home, while George must meet his parents by 6:15 to take them out to celebrate their anniversary. Also, Jerry has to go to the bathroom badly.
While the gang searches for the car, Elaine desperately begs people in the parking garage to offer them a ride around the building to find their car, but no one is willing to help or has any sympathy for the goldfish. As for Jerry, he is eager to urinate. Kramer encourages Jerry to do it in some dark corner where no one can see him. After Jerry reluctantly does so, he is spotted by a security guard and is held in the guard's office. Jerry tries to talk his way out of trouble by making up a story about a fictional disease of "uromysitisis", but the guard is not convinced; Jerry makes up some other stories, but the guard is still not convinced. Meanwhile, Kramer, Elaine, and George wonder where Jerry is, so Elaine goes off on her own to find him; Kramer and George decide to do the same. Later, George also gets caught in the act of urinating, after being convinced to do so by Kramer. Both Jerry and George are fined and released. After the two find Elaine, Jerry convinces George to ask an attractive woman, whom they saw earlier in the episode, to offer them a lift around the garage. After the woman accepts without hesitation, the gang all enter into the woman's car and drive off, but moments later, the woman kicks them out after George said something to the woman that makes her explode in anger (the viewer is not told exactly what George said to the woman, but it involves L. Ron Hubbard and Scientology). Then by luck, the gang is dropped off right by Kramer's car but unfortunately, Kramer, who has the car keys, is still lost somewhere in the garage.
Hours pass by as George, Jerry and Elaine wait. Finally, Kramer shows up, having gone on his own hunt for the air conditioner because he forgot where he left it. Elaine's goldfish have not survived and George is well past the time deadline to meet his parents. As they all enter the car, the engine fails to start.
Production
The Parking Garage was written by Larry David, his 4th writing credit for the season and was directed by Tom Cherones, his 4th directing credit for the season. The episode was difficult to write and create as it all had to be done on the normal Seinfeld soundstage. Jerry's apartment and the studio audience seating was removed. Every shot used showed the entire set so it constantly required shooting from different angles. Mirrors all around the perimeters of the stage gave the illusion of further depth and with just a dozen cars, the illusion of being in a giant parking garage was complete. The end was scripted to have the gang drive off together. The car failing to start at the end of the episode was an accident. An old car was used, and when it did not start, it was decided to keep it in the episode as something else going wrong. Jason Alexander and Julia Louis-Dreyfus can briefly be seen starting to laugh when the car didn't start.