Since 1998 the Boston Underground Film Festival has featured films that are weird, experimental, esoteric, and flat-out fun, and their documentaries are often the most exciting and original offerings in the program.

This year the festival includes two nonfiction films that push the limits of the genre: Neil Edwards’s “Sympathy for the Devil: The Story of the Process Church of the Final Judgment,’’ about the 1960s cult group (screens March 26 at 12:30 p.m. at the Harvard Film Archive, with the director present), and Ross Sutherland’s “Standby for Tape Back-Up’’ (screens March 26 at 2:45 p.m. at the HFA, also with the director present), a live performance/documentary fusion. Though they differ widely in style, both films deal with systems of meaning, of how we organize experience in order to avoid the abysses of chaos and paranoia.

Edwards’s film investigates a cultural, or subcultural, manifestation of that drive, a group that tried to invent and market a mythical system to those avid for transcendence.

Had you been in Harvard Square in the late ’60s you might have been approached by a caped person dressed in black, most likely a youth with a Christ-like beard and a piercing stare (they had been trained to stare without blinking). He would have asked you to buy a superbly designed magazine, its cryptic text and illustrations rendered in red, black, purple, and gold. It would be the eponymous publication of The Process.

“What is The Process?’’ is a running question throughout the film, usually asked in an animated image from the magazine itself. The short answer is that it was a cult started in London by Robert De Grimston, a bright, charismatic Londoner, and his wife, Mary Ann MacLean, an enigmatic ex-prostitute from Glasgow. Former Scientologists, they drew together other bright (and well-to-do) seekers to their circle and led them on a pilgrimage that took them from London to Mexico and into the hipper communities of major American cities — until the couple’s messy divorce ended it.

Was it all a scam? Perhaps, say former members of the group interviewed by Edwards, some still bearing a satanic, majestic mien as they enter old age. But it was also the most meaningful experience of their lives.

Sutherland’s film is equally searching and driven by unanswered questions, but it is personal rather than evangelistic. He starts with the proposition that when Pink Floyd’s album “Dark Side of the Moon’’ is played as the background for that ur-text of Western pop culture, the 1939 film version of “The Wizard of Oz,’’ the two merge with uncanny synchronicity.

Then he refers to a videotape left to him by his beloved grandfather. It includes a scene from “Ghostbusters,’’ a film which his granddad took him to see when he was only a child. The experience terrified and enlightened him. The rest of the videotape is a palimpsest of TV shows recorded over one another, one of the most prominent being “The Fresh Prince of Bel-Air.’’

Of such things are philosophies made. Sutherland will be there in person to perform live the film’s poetic voice-over — a mix of deconstruction, Proustian recall, and hip-hop.

The 18th Boston Underground Film Festival takes place March 23-27. Go to www.bostonunderground.org.

Peter Keough can be reached at petervkeough@gmail.com.