“Woodlands Dark and Days Bewitched” is a documentary about the history of “folk horror,” a film of almost breathtaking thoroughness in exploring what that term means, the shared pagan stories that span the globe and inspired it, and the movies in cultures all over the world that have spun out of this tradition.

If you’re a fan of the genre, which takes in films from “The Wicker Man” and “Midsommar” to pretty much anything with a witch, demons, shape-shifters or a rural setting, settle in for sometimes brilliant, often pithy explorations of where or that piece of folklore, these traditions and all those films came from. Maybe watch “Woodlands Dark” in chunks, as it is an awful lot to take in and you won’t want to miss much of its over three hours of study.

Writer-director Kier-La Janisse begins with the British obsession with the genre, with fans, journalists and experts of various persuasions placing the boom in the genre — it dates from near the beginning of cinema, but really hit its stride in the 1970s — within cultural tradition and historical context. We learn about the literary forebears who invented it (think “Legend of Sleepy Hollow” among others).”

And then the documentary expands, like the horror genre it’s about, to envelop the planet. Not many cultures aren’t represented in the movie’s vast survey of global folk horror cinema.

As its core, folk horror is a “return to the Olde Ways” friction between rural and urban, something that emerged when many first fled for the cities during the Industrial Revolution, but which blew up again as people abandoned cities in the Earth Day (US) and “back to the land” youth movements of the ’70s.

As tropes of the genre are trotted out in their many different forms, film scholar David Howard Ingram lands what I thought was the money shot. These movies are about times long past, times recently past and times right this minute. They’re about “modern” aka “urban” people and their educations, their belief in science, vs. “traditional” people, be they from rural Britain, Appalachia or anywhere mask mandates and vaccinations not ordained by their cult leader are protested and avoided.

“‘We don’t go back,'” Ingram says, quoting a man-of-science in an obscure horror film sampled here. That’s “the fundamental tension of ‘folk horror,'” this notion that returning to ancient, generally pagan rituals, traditions and superstitions is not in the cards for the modern people (the viewer’s surrogate) often trapped in “Midsommar,” waylaid by “The Witch” or “other” folks fearing this “tradition” or that belief.

We track through the decades in which “witches became cool again” in the culture, and on screen, when “The Candyman” made his bow or “La Llorona” first sheds her tears in Old Mexico…and Japan and other places which have a “mother who drowned her own children” legend.

This film is a crash course in this corner of horror, and a must-see for fans or even those curious about the many ways this pull towards the pagan manifested itself over in movies over the decades. A pretty good chunk of the horror coming out now spins out of “The Babadook” or “Witcher” or assorted witch hunters and primal sacrifices, with Netflix and Amazon full to the brim with offerings in the folk horror genre in film or limited series form.

But being this long and broad in scope, “Woodlands” can’t help but feel repetitive — exhaustingly-so.

It’s fascinating to see the similarities folk myths share among many cultures, the ghosts, shape-shifters and witches of Britain and Japan, Czechoslovakia, Brazil, Mexico, Russia and North America. A

Yet at some point, as the movie see-saws between clips and references to celebrated and/or popular and iconic films — “The Wicker Man,” “Lair the White Worm,” “Midsommar” and “The Amityville Horror” — and more obscure titles like “Hex” and “Edge of the Knife” and “A Field in England,” it all starts to seem like a contest between the scores of interviewed filmmakers, genre obsessive authors, festival organizers and the like.

“Ah, but HERE’s one YOU’VE never heard of.”

And as the film goes on and on, through its second and third hours and starting on its fourth, the broadening definition of “folk horror” takes in titles that make you scratch your head while leaving out this obvious “Indian burial ground” title (“Poltergeist”) or skipping over that folklorish found footage blockbuster “The Blair Witch Project.” At times, it’s so broad as to seem almost meaningless as a subgenre.

There are dazzling experts who plainly know their subject, and a giggling critic, a stumbling Brit who refers to a title as “the Uber text” or a particular subgenre, and this other bloke who insists we credit him — insists REPEATEDLY — with coining the term “folk horror,” when as he himself admits it pre-dates him using it by nearly a century.

None of which should scare you away, especially if this genre is your jam. But take seriously that suggestion that you don’t immerse yourself in “Woodlands Dark and Days Bewitched” in a single sitting. Taken all at once, the film’s aesthetic, informational and entertainment virtues lose a lot of ground to “Right, we GET it” and “Why didn’t you edit this to something more compact and less repetitious?” attitudes.

Rating: nudity, violence

Cast: Alexandra Heller-Nicholas, Alice Lowe, Piers Haggard, Robert Eggers, many others

Credits Scripted and directed by Kier-La Janisse. A Shudder release.

Running time: 3:14