When U2’s “Achtung Baby” debuted in November 1991, it was the culmination of an emotional and conflict-filled journey for the hugely successful band. The rockers from Dublin had fallen from grace after delivering the critically panned album “Rattle and Hum,” and had lost their way musically, after an overexposure to American roots music. "Achtung Baby" had the formidable task of reinventing U2 -- if the album failed, it could have marked the end of the beloved band headlined by Bono and the Edge.

Obviously, we know the outcome. But the journey is what documentary filmmaker Davis Guggenheim set out to capture in “From the Sky Down,” the opening-night film at the Toronto International Film Festival on Thursday. It's an unusual selection by festival organizers, who typically program a Canadian film for opening night.

Guggenheim, who had previously worked with the Edge on the 2008 doc “It Might Get Loud,” was interested in the story of the band at a crossroads. And he had complete access to U2’s comprehensive archives, in addition to footage from an ill-fated documentary about the band's experiment with  American music. Guggenheim said he was surprised by the amount of access the band gave him during the six-month period he had to make the film.

“There’s this really great moment from the film when they are on tour, this Lovetown tour, where they have traveled all across America with B.B King. And they come back to Ireland for the last show, on New Year's Eve, at the end of the '80s. They are counting down the clock and they realize as they are performing their music in front of their Irish fans that they had completely lost their way,”   Guggenheim said in an interview.

“What’s so fantastic about the story is it’s about artistic reinvention," he added. "They are the No. 1 band in the world and their fans are expecting another 'Joshua Tree,' and they gave them 'Achtung Baby,' which was musically completely different. ... Bono says in the movie, 'We needed to take a chainsaw and cut down "The Joshua Tree." ' ” 

Guggenheim, who won an Oscar for directing the environmental documentary "An Inconvenient Truth" and who most recently directed the education documentary “Waiting for 'Superman,' ” said “From the Sky Down” is for more than just fans of U2.

“It’s for anyone who is interested in how songs get written,” said Guggenheim, adding that the title comes from how Bono describes their songwriting method. According to Guggenheim, the band improvises together and out of those sessions come “these magic moments that they tie together.”

He added: “It’s kinda backwards. No one else does it this way and out of it comes these really unique U2 songs. So if you’re into music and you wonder how people write songs, it’s utterly fascinating.”

The film is timed to coincide with the 20th anniversary of “Achtung Baby”; following the festival, the movie will be shown on Showtime.