After a successful inaugural year in 2016 that featured the likes of Rolo Tomassi, Textures, Igorrr and Destrage, Complexity Fest is back to dish out a second helping of heavy, technical progressive music.

The one day, indoor event is held in the idyllic, tranquil, picturesque city of Haarlem, just 12 miles west of Amsterdam.

With its stunning architecture, rich history and elegant waterways, the city evokes a charm and serenity reminiscent of the Dutch capital, albeit with just 150,000 citizens compared to Amsterdam’s 800,000 or so and rising. It feels like an unlikely location for one of the latest in a long line of tech-metal festivals designed to sate the average heavy music connoisseur’s appetite for bowel-shaking riffs set to brain-frazzling polyrhythms.

But the Patronaat proves a perfect venue; over the course of 13 hours, 22 bands play the music hall’s 3 stages and with a main room that facilitates just 1,000 patrons, the atmosphere is incredibly relaxed, no doubt partly due to the carefree Dutch sensibility and partly due to the herbal haze that hangs heavy like a fog in the Patronaat’s plentiful smoking rooms.

Despite the insinuations that the festival name might conjure, the line-up’s not exclusively limited to million-note-a-minute djent bands that are barely distinguishable from one another.

All corners of the metal spectrum are covered, whether it be the brutal grindcore of Beaten to Death, complex instrumental math-rock courtesy of Mutiny On the Bounty, the progressive deathcore of Humanity’s Last Breath or the post-hardcore trappings of the UK’s very own Napoleon. With so much to cover, here are the highlights of Complexity Fest’s second year.

(Cas Kerkwijk (Cas Kerkwijk)

Possibly the darkest, most savage thing to come out of sunny Orlando, Florida since the emergence of the state’s burgeoning death-metal scene in the late 80s / early 90s, Arms make a gloriously obnoxious racket that reverberates around the tiny bar acting as Complexity’s third stage.

Their crust-punk inflected post-hardcore isn’t for everyone, as is evidenced by the small pockets of people that sporadically leave with grimaces on their faces, but it makes those who stay warm to the band even more. The idiosyncratic sound is a lot to digest; elements of mathcore, noise rock and thrash are all viciously blended in to the mix to create a chaotic maelstrom which is not for the faint of heart.

Despite the pandemonium, at their very best Arms evoke the spirit and intelligence of metallic mathcore pioneers Coalesce and Botch. If they can fire on all cylinders and reach those heights with more frequency, we could be talking about a very special band.

It’s taken a hell of a long time for the UK’s Bossk to get where they are today. The stoner post-metal quintet originally formed in 2005, released a couple of EPs then split up in 2008, before reforming with a slightly altered line-up in 2012. Their potential as a band had been simmering in the underground for years before finally boiling over last year with the release of their marvellous debut full-length album Audio Noir. Their presence as an instrumental outfit is so captivating, it’s initially a shock to the system when vocalist Sam Marsh strolls out roughly 20 minutes into the set and starts howling like a stuck pig.

But Bossk are adept at beauty as well as pain, as the shimmering, gorgeous opening riff to set-closer Kobe testifies. Their dalliances between light and shade are what make them such an all-conquering force ... let’s hope we don’t have to wait as long for album number two.

Agent Fresco vocalist Arnór Dan Arnarson has the 'ability to sound like a wailing banshee one moment and a chorus of angels the next' (Bete Photography)

Agent Fresco stand out as an oddity on a bill made up of atypical bands and as a result play one of the very best sets of the festival. On the surface, the Icelandic quartet don’t have the heavy cojones of their contemporaries found elsewhere on this line-up, but when they do unleash hell, on the likes of the explosive He Is Listening and utterly devastating Angst, it’s an existential howl of despair quite unlike anything you’ve ever heard before.

Summing up the band’s sound is so difficult most don’t even attempt to, but there are elements of Sigur Rós, The Dillinger Escape Plan, Muse, Biffy Clyro, Anathema and Rolo Tomassi all mixed up so vigorously, Agent Fresco emerge sounding like their own proposition entirely. See Hell and Dark Water are both stunning examples of anomalous, quirky unorthodox songs bolstered antithetically with pop hooks which are nigh-on-impossible to dislodge from your brain. It is the contradictions in Agent Fresco’s music that make them so utterly compelling.

Vocalist Arnór Dan Arnarson’s stunning ability to sound like a wailing banshee one moment and a chorus of angels the next is a constant source of astonishment whilst Þórarinn Guðnason is constantly switching between guitar and piano throughout, playing both with consummate ability. For all this technical prowess however, Agent Fresco always ensure that the quality of song-writing is paramount and they deserve to be lauded as one of the very best, most unique voices in modern music.

Frontierer play an absolutely jaw-dropping set of savage technical 21st century metal that paradoxically manages to combine the pummelling, staccato onslaught of Meshuggah with the loose, jagged untamed chaos of The Blood Brothers. Their amalgam of complex counter rhythms and whammy-inflected lunacy is a forceful rebuttal to anyone who thinks metal has lost its edge or is incapable of evolving after almost 50 years as a genre.

Like Hendrix, Dimebag and Morello before them, guitarists Pedram Valiani and Dan Stevenson approach guitar in a way that completely and utterly boggles the mind, extricating un-earthly, hitherto unimaginable sounds out of seven strings and a hunk of wood.

Though the music Frontierer play is too abrasive to ever reach the popularity of Jimi Hendrix, Pantera or Rage Against the Machine, Valiani and Stevenson’s names deserve to be whispered in hushed tones alongside modern guitar heroes such as Benjamin Weinman, Tosin Abasi and Brent Hinds. For 9 songs and 45 minutes, the audience is completely stunned into submission by the sheer overbearing majesty of the Scottish / American quintet, and patrons stumble out of the room dazed and stupefied but secure in the knowledge they’ve just seen something totally awe-inspiring.

Frontierer guitarist Dan Stevenson gets up close and personal with Complexity's crowd (Cas Kerkwijk)

Black metal icon turned progressive madcap experimentalist Ihsahn is quite easily the most anticipated act of the day and the biggest draw Complexity Fest has managed to book in its brief history. The ex-Emperor frontman’s musical focus has broadened and blossomed into avant-garde exploratory pastures; with a pool of six diverse albums to draw upon, the set is a multi-faceted, idiosyncratic feast for the senses.

The classic rock stylings of Until I Dissolve, a cut from Ihsahn’s latest album Arktis., translates perfectly to the now far-beyond-sozzled Dutch crowd and an early set highlight comes in the form of A Grave Inversed, an amalgamation of guttural vocals, blast-beats and saxophone that is about as bonkers as progressive black metal currently gets.