Goin' Down to South Park is a mockumentary which covers the making of the show South Park in a fictional fashion. It first aired on Comedy Central on May 3, 1999.
In the documentary, the creators pretend to be arrogant, obnoxious jerks who are only in it for the money, spoofing similar such shows. The documentary consistently refers to Trey Parker and Matt Stone as "kids" even though they are actually adults. Trey and Matt spend the entire documentary in a hot tub with Martin Cendreda, one of the show's animators.
The show also explains how the creators got Isaac Hayes to play Chef. They tell that he originally didn't know what the cartoon was all about, even though the creators thought he knew. When he found out, he was originally thinking of leaving but changed his mind so he could see what Trey and Matt could do. The documentary also told that Isaac was worried about getting sued for the Chocolate Salty Balls song. They say that one guy thought it was actually about testicles.
The documentary is a special feature on South Park: The Complete Second Season.