In 1997, WTTW went deep inside the Second City's mainstage, producing an hour-long documentary about the Paradigm Lost revue. Three future 30 Rock cast members—Tina Fey, Rachel Dratsch, and Scott Adsit—appeared together, along with future writers Kevin Dorff (Late Night with Conan O'Brien, Review) and Jenna Jolovitz (MADtv), and the late jack-of-all-trades Jim Zulevic.
For a documentary about an improv revue, it's very earnestly in the PBS style, but there's something to that as well. When director Mick Napier describes what a truly elite improv actor is capable of, his answer is something of a surprise: "The best improvisers in the world probably get up an 80, 85 percent success rate. Success equalling having a scene that builds, a character that works, having the audience enjoy that. Not necessarily laughing, but being empathetic to a process that's heightening in the scene."
The video quality is unfortunately vintage late-'90s VHS, but it's compelling nonetheless (via Vulture's Margaret Lyons).