Every now and then, a friend will clue you into something that you really should have known about for an embarrassingly long time. Well, let us be a friend to you now: you really need to know about OFF Festival in Poland. A three day weekend in the Southern city of Katowice every August, it is one of Europe’s best-kept secrets. More than most festivals of its size (up to 15,000 people a day), it is committed to curating line-ups that are comprised of challenging, cutting-edge, progressive artists. It does not appear to need to lure in major middle of the road names to pay for its existence; it just knows that enough outside-the-box music fans will come from far and wide every year to make the thing a success.

Friday is ushered into life by Nanook of the North, a new collaboration between two acclaimed Polish artists, Stefan Wesolowski and Piotr Kalinski. Their one major work to date is a retrospective musical score for the landmark 1922 film documentary that they take their name from. The film tells the tale of an Inuit family as they go about their regular lives, but with this new soundtrack the images, which are displayed behind the duo as they play, take on a contemporary, strangely eternal majesty. They reimagine a hundred-year-old setting with ambient electronic textures and plaintive violin lines, and the crowd sit and stand in perfect, reverent silence, experiencing this performance internally. It is the start of a weekend-long trend: the OFF crowd are some of the most knowledgeable, respectful music fans that you can find anywhere around the festival circuit.

Over on the Trojka Stage is a rare live sighting of The Mystery of the Bulgarian Voices, the excellent cult record of the Bulgarian State Radio & Television Female Vocal Choir that was introduced to a wider world in 1986 on a re-release by 4AD. It is the sort of music that is only mentioned in hushed reverie by music aficionados everywhere, but it draws a sellout crowd at this tent. The stage sees a line of nearly twenty women, dressed in traditional Bulgarian clothing, with two flanks of musicians either side, including folk drums and balalaikas. Occasionally, one or two vocalists will step out of the line and take the lead, frequently leaving a tearful hush hanging over the crowd. There is a historical fortitude to the set, a beauty that has been crafted and perfected for longer than any one person can live, and it is humbling to watch.

The Friday headliner is M.I.A., perhaps the biggest single star and the festival, and perhaps the biggest single disappointment. Her set is wonky, disjointed and unfocused, a meandering trip through her back catalogue that seemed to leave the artist as confused as the audience. Far more successful on the night is Jon Hopkins in the late slot on the Forest Stage. By clear water, he creates the biggest sound of the weekend, his bass-heavy beats exploding in the night sky with just the merest flick of his finger. One can only imagine the power rush he must feel to hold so many people’s consciousness in his hands. We hear tracks from both ‘Immunity’, and ‘Singularity’ and no question familiarity plays a part, but this is direct, primal engagement with sound and nobody is standing and waiting for their favourite song.

Saturday starts with perhaps the buzziest of the many Polish bands on the bill, Coals. The local duo made up of vocalist Kasia Kowalczyk and Lukasz Rozmyslowski, trade in moody, darkwave music that is labelled too often as dream pop. They’d surely more quickly evoke nightmares. However, they are curiously all decked in white, from their glasses to the drapes covering their mic stands. It is a juxtaposition that speaks to their whole identity: Kasia is, in fact, a fairly timid character in real life, but on stage she is a fearsomely composed, enigmatic presence. They explore elements of feedback and sonic tampering in their set, and despite minor technical difficulties, they prove why they are making waves internationally.

Japanese psych noise mainstays Bo Ningen bring their cacophony to the Experimental Stage as a late replacement for John Maus. They may have been a late call-up, but either this crowd are so deep into alternative music culture that they are already entire au fait with the band or they are so hungry for the outer reaches that they immediately fall hard for them. Every time the band aren’t in full-on rip mode seems like a waste, and while they actually start with a fairly mild track, they soon reach top gear, and frontwoman Taigen Kawabe is in full-on animal mode, hair flailing, guitar stripping the outer layer of everyone’s eardrums.

The mood is considerably changed for Saturday headliner Charlotte Gainsbourg. In some senses she is the most mainstream presence on the bill this year, her warm electro-pop very easily digestible. There is great enthusiasm nevertheless, and her grace on stage is immediately engaging. She centres the set on tracks from 2017 album Rest, but special mention must go to her touching performance of ‘Charlotte For Ever’, a track from her debut album in 1986 that she originally performed in duet with her father Serge Gainsbourg. Her interpolation of Kanye West’s ‘Runaway’ takes the audience by surprise, not least that such lyrics would come from her mouth, but she finds the transient beauty in them in the same way that she does in her own compositions.

Everybody’s favourite reliable pan-festival experience, the gently brooding Sunday lunchtime singer-songwriter, is provided at OFF 2018 by Daniel Spaleniak, here to awake us from our slumber. He plays with a backing three-piece, and his songs don’t insist on intruding into your personal space, but possess a dark, dramatic weight if you have the strength and curiosity to explore, thus making him the perfect fit for this coveted slot. Daniel welcomes Kasia from Coals onto the stage for a couple of numbers to provide a vocal atmospheric synthesiser role. For those with an intact attention span, the riches are there to enjoy.

A stronger constitution is required for No Age’s arrival though. The Los Angeles duo are as tight as they come, playing their compressed, distilled version of garage punk that has brought them success for a decade now. They have fond memories of OFF, having previously played in 2011, and although guitarist Randy Randall is nursing a wrist injury from a rock’n’roll high five that went wrong in London the previous night, the intensity is remarkably high. His opportunities to indulge in searing guitar noise are limited, but when the chance arrives, he packs a turbo punch. By the time they wrap up with ‘Teen Creeps’, they have left an indelible mark on the Silesian landscape.

After a bizarre foray into the world of Ariel Pink and his conflicted, confounding stage presence, which alienates as many in the crowd as it attracts, Sunday on the main stage is rounded out by Brooklyn indie veterans Grizzly Bear. Their dense, multi-layered studio creations are a tall order to recreate in a live setting, but then they’ve been at this for a while now, and their meticulousness extends just as fastidiously to stage arrangements as to studio. Nine years have passed since their landmark release ‘Veckatimest’, but it doesn’t stop them from letting it get more than its fair share of the setlist, and these are the tracks most gratefully lapped up by the audience. After three days of indulgence and exploration, their mellow, enchanting, interlocking melodies are the perfect note on which to end the weekend.

There is a paralysing array of festivals vying for your attention each summer, large and small, established and new. They will sell themselves to you on often dubious means when in reality too many are interchangeable. On this occasion, OFF Festival legitimately offers something that is hard to find: a festival fully populated by both artists and audience members that have signed up out of love for exploring the outer reaches of popular music. It is a model that will only work if enough like-minded people show up each year, so if this sounds like your cup of tea, make a note for next August.