(Denver-based NCS writer Gonzo enjoyed a glorious couple of nights at the inaugural edition of Flatline Fest on June 13-14, and delivered to us the following enthusiastic report, accompanied by photos made by Jacob Juno.)

For heavy music, the US festival circuit is quietly growing into something that defies conventional logic. Recent years have seen the unlikely resurrection of vaunted gatherings like Milwaukee Metal Fest, while longer-running affairs like Maryland Death Fest and Northwest Terror Fest proved that even a global pandemic wasn’t enough to douse their fires for good. And deep in the wilderness outside Glacier National Park, the Blackfeet Indian Reservation enshrined a new kind of heaviness with the 2025 incarnation of Fire in the Mountains.

Obviously, these events don’t just spawn out of thin air. They’re the collective result of dedicated people putting ungodly amounts of time, energy, and creativity into something they all believe in, often at the expense of their own sanity.

But in the end, these festivals are more than just a few days of bands playing songs. They’re community gatherings where occasions are celebrated, longtime friends meet up, new friends are made, and the best kind of chaotic merriment prevails.

Evidently, nobody knows this better than Denver producer Dave Otero and co-promoter Chelsea Lowe, whose first-ever Flatline Fest at Denver’s Oriental Theater last weekend turned out to be a masterclass in how to throw one hell of a fucking party.

Taking its moniker from Otero’s own recording studio, the idea for Flatline Fest began with the simplest and purest of intentions, as Otero told Denver’s Westword earlier this year: 

“I’ve collaborated with every band in this lineup in the studio over many years and have always wanted to put something like this together,” he says. “The fest is a chance to celebrate those friendships in one of our favorite independent venues.”

Otero’s Flatline Studios has been a cornerstone of recording heavy music for decades. Having the built-in community surrounding the assembled lineup seemed like an early indicator of massive success for the two-day event, so it was no shock to me that people travelled internationally for this, and even less of a shock that the festival sold out both nights.

DAY ONE: SATURDAY, JUNE 13

I walked into the Oriental Theater on Saturday afternoon just in time to see longtime crossover outfit Clusterfux play the final few songs of their set; the stage was rife with sweaty bald heads and tank-top-clad torsos at 5 pm. As Denver’s longest-running hardcore punk band, the five-piece sports a sound that’s part Agnostic Front and part DRI, and each song immediately tested the limits of the venue’s sound system. With a rap sheet that includes sharing stage time with both aforementioned bands, Clusterfux’s straightforward, no-bullshit approach was an ideal opening act for what was to come.

Also, the venue being shockingly packed at 5:30 pm was a great sign. The metal scene here is full of die-hards who show up early, and the crowd size was already well on its way to continuing that trend.

Homegrown sludge merchants Glacial Tomb were next up, with the multi-talented mastermind Ben Hutcherson leading a ferocious 30-minute barrage of razor-sharp riffs and skull-crushing blast beats. I don’t know what he’s been feeding his bandmates these days, but this outfit has never sounded better. “Sytgian Abattoir” from 2024’s Lightless Expanse was enough to ignite the weekend’s first pit as the crowd slowly continued filling up the floor. New-ish drummer Joey Spates pounded the kit like it insulted his mother, while Hutcherson’s grimy shriek could’ve peeled the wallpaper off every corner of the venue.

I’ve somehow found myself at a show that includes Nashville’s Inferi at least five times over the past few years. It’s a happy accident. This was the first time I’d seen them since the new album Heaven Wept came out in April. If there’s one thing Inferi can do, it’s make the absolute most out of a 30-minute set. By the numbers, it included two tracks from the new album that I counted (“Godless Sky” and the title track), three tracks from previous albums, and at least one inflatable T-rex that seemed to manifest in the pit from an unseen void.

Right around then, a large man in a chicken costume showed up and riled up the pit. This wasn’t my first Chicken Man sighting in Denver, and I strongly doubt it’ll be the last.

The festival was starting to take shape in front of my eyes in real time, assembling its true form with each passing hour. After being part of several multi-day metal festivals in Denver, though, this was what I came for. Jesus, I thought, this place is the most affable kind of weird. And it was about to get even fucking weirder.

The masked brigade known as Nuclear Power Trio, which is a) rumored to contain members of Cephalic Carnage and Allegaeon, and b) features three members in Putin, Kim Jong Un, and Trump masks, stormed the stage for what was, incredibly, their live debut. As they ripped into tracks like “W.A.P. (Wet Ass Plutonium)” and “A Clear and Present Rager,” the venue vibe went from “slightly riled up” to “is this actually a Gwar show?” in approximately 15 seconds.

This idea might’ve started as a trio, but a more appropriate description would’ve been “Nuclear Power Ensemble.” Keyboards (played by the Queen of England, because why not), saxophone, more guitars, and a screen playing clips of another masked dude taunting the crowd catapulted this set into completely insane territory. It’s not clear how long this band has been plotting this night in some subterranean superhero cave, but much like this festival itself, it’d be a goddamn tragedy if this were the only time they’re ever doing it.

While I was pondering this mystery, the stage crew was preparing the grounds for the next sonic onslaught. It’s one thing to get a bunch of local and regional bands to show up to play the first run of a festival, but getting the members of Aborted to fly in from Belgium and Iceland is pulling some serious cred.

Just then, I felt an intrusive thought creeping in, and I was powerless against the twisted urge to blurt it out.

“Y’know,” I said to my friend, who was just standing next to me trying to enjoy himself, “what if Aborted toured with Ingested and Dying Fetus? Would they just call it the Circle of Life tour?”

He blinked, grinned, and shook his head. “They pay you to think like this?” he asked.

“Christ, I hope not,” I replied. “But enough about that. Who else would be on that tour? I need ideas, dammit!”

With cosmically perfect timing, a guy wearing an Infant Annihilator shirt squeezed by us on his way to the front. Somewhere, Satan laughed.

Aborted were simply electric. The razor-sharp guitar tone could’ve cut through glass, and the surgical precision of the syncopated guitars and the kick drum was so in sync that they could’ve been literally joined at the hip. “We flew 20 hours to get here, Denver,” vocalist Sven de Caluwe said between songs before giving a requisite shout of appreciation to Otero and Lowe.

Somehow, this was my first time seeing Aborted live, and the performance was more than enough for me to start digging into their discography more deeply than before. The lack of a bassist on stage didn’t hamper their sound a single bit.

Before we knew it, the moment we’d all been waiting for was upon us: Vancouver’s Archspire would soon take the stage to blast our heads clean off our shoulders. I’d seen the Canadian virtuosos play this very stage years ago, but this time it already felt bigger. The anticipation was in the air long before the lights went out.

From the moment the devastating warp-speed opening blast beat of “Drone Corpse Aviator” pounced on this crowd, the night belonged to Archspire. Wielding the most intimidating musical instrument imaginable, bassist Jared Smith’s ability to tame that beast was a sight to behold. But then again, how the axe-slinging duo of Dean Lamb and Tobi Morelli can also play this fast while being so technically precise might be the eighth wonder of the world. All this is to say nothing of Ollie Aleron’s indecipherable vocal barrages driven by new drummer Spencer Moore’s ritualized kit abuse.

How this band plays at this unfathomable speed while staying in sync with each other is something we should all feel lucky to witness.

And I may have seen Archspire a few times before, but this was the first time I’d been in a wall of death that was divided by circumcision status. It was also the first time I’d seen two guys being dragged on stage to chug a PBR out of their own boots. Truly, this was an evening of firsts. “Human Murmuration,” “Involuntary Doppelganger,” and “Golden Mouth of Ruin” all but ensured I’d be wide awake long after I’d leave the venue until I’d be ready to do it all again tomorrow.

Overall, the experience of Archspire devastating this crowd was like freebasing jet fuel while getting a cocaine enema. Day two already had its work cut out for it.

DAY TWO: SUNDAY, JUNE 14

The Denver heat was growing intense this afternoon, so the dark, cave-like atmosphere of the Oriental Theater was an alluring break from the unforgiving UV index outside. My Pacific Northwest blood still rebels in silent rage whenever the temperature climbs above 85F.

I slithered into the venue to catch local melodeath act Necropanther doing what they do best: Play dizzying riffs. At four albums deep, the band has found itself on what feels like a precipice of something bigger. They’ve opened for other festivals like 2024’s Decibel Metal & Beer Fest, turning more heads on more stages in the process. Their speed, precision, and tight songwriting have always reminded me of the best of Skeletonwitch.

Most of this festival had been shaped by sheer speed and frenzied tempos so far, which made local doom trio In the Company of Serpents stand out from the pack. As the only doom band on the bill, I wasn’t sure how the crowd would react to something on the opposite side of the metal spectrum from tech death.

But then I remembered this is still Denver, and in this scene, “out of place” is a concept that doesn’t exist. As Serpents settled into their set, bassist/guitarist Ben Pitts milked the intro of “Buzzard Logic” long enough to let the dust and twang of the Denver sound breathe for a while. When vocalist/guitarist Grant Netzorg and drummer Andy Thomas joined, it had all the power of a thunderclap echoing across a barren desert landscape. “Don’t Look in the Mirror” even got a pit going at the improbable hour of 6:15 pm.

It was an engrossing 30 minutes. Grant later told me he was squinting at my Northwest Terror Fest hat, wondering if it was in fact a Southwest Terror Fest hat, while I was squinting back, trying to figure out if he was wearing a bolo tie. (He was, and few men can pull it off better than he can.) After the set, I wandered over to the merch booth and followed up on the exchange by asking Grant and Ben if I could start affectionately referring to their music as “bolo tie metal,” and I don’t think either of them hated it.

With The Zenith Passage coming up next to rip everyone’s head off at warp speed, slower tempos would soon vanish like a fart in a wind tunnel. The band wasted no time, as usual, by absolutely dominating the stage with the opening salvo of “The Axiom of Error.” That opening breakdown by itself is enough to send the average concertgoer through a wall like some kind of six-string Kool-Aid Man, and the following 28 minutes weren’t any different.

Brandon Giffin’s bass immediately joined the ranks of Archspire’s Jared Smith in the “Most Intimidating Musical Instrument” contest that I’d decided was now a thing. Using their thick-necked behemoths of choice, both of them played the most technically complex music imaginable while barely breaking a sweat. Giffin, vocalist Derek Rydquist, and guitarist Justin McKinney—the three former Faceless members in Zenith Passage—are letting their creativity and prowess fly to heights unreachable by most, and they got so caught up in their set that they unfortunately had to cut “Datalysium” from the end of it. Even still, this was a very small complaint for a set this good.

It’s hard to have a bad time during a Cephalic Carnage set. Len Leal wasted no time on the mic, relentlessly shouting for a call-and-response of “WEED!” in between some of the most insane vocal work anyone had heard all weekend. The band even reached back to 1998’s Conforming to Abnormality with “Jihad,” whipping up the pit into a vortex of spikes and leather, while closing track “Lucid Interval” had everyone feeling the elevation.

DRI’s Danny Walker was tagged in on drums, pounding out kit gymnastics with impunity. It’s weird to think this band hasn’t recorded anything new since 2010, but none of it mattered. Cephalic Carnage continues to be as relevant as ever, and I can’t see that changing even if they never record anything again.

To this point, this festival showed us that speed fucking kills, and it always will. This would only continue with the formidable Allegaeon taking the stage. Last year’s The Ossuary Lens was a ripper of an album, and 2022’s Damnum was even better. But this would be the first time I’d be seeing the band with original screamer Ezra Haynes back on the mic, so I was intrigued from the start.

The set was impeccably played, and nobody would argue with that. “Chaos Theory,” “The Swarm,” and the live debut of “Dark Matter Dynamics” all absolutely crushed, with each song selection seemingly chosen to out-shred its predecessor. The band even brought guitar maestro Adrian Bellue out for the latter, injecting some classical guitar/flamenco flavor into a track rife with complex riffs. At seven albums deep, the only question left for Allagaeon to answer is whether they can continue outdoing themselves.

This evening was zooming by at speeds only matched by the music itself. There was a buzz in the air as the crew for Cattle Decapitation began the set change, and rightfully so. The band literally sold out of merch halfway through the night, prompting me and a gleeful Ben Pitts to capitalize on the empty space by using it to drink IPAs.

This was probably the smallest venue the extreme deathgrind outfit had played in a while, and vocalist Travis Ryan would later tell us this would be their last show of the year. Then, he said, they’d be returning here to Denver to record their next album at none other than Flatline Studios, with Otero once again behind the boards.

The set itself was filled to the brim with the kind of blistering energy that only extreme metal can deliver. “Bring Back the Plague,” “Scourge of the Offspring,” and “Vulturous” reminded me how both Death Atlas and Terrasite are 10/10 don’t-skip-a-single-song amazing. If stage antics are any indication, Travis Ryan has only gotten weirder with each album’s release, no doubt pleasing whatever vegan mutant god they’re obviously working to appease.

Right before their set, the Carolina Hurricanes won the Stanley Cup, and the dude wearing a Canes jersey in the pit was having the best night of his life. That energy was unignorably contagious.

By the time this night ended, there wasn’t a single face in the venue that didn’t have a shit-eating grin plastered against it. The bands were outside by the Brutal Poodle food truck, reveling in the feeling of playing a small festival where there were more friends than strangers. As the crowd poured out of the venue, few people actually left right away. The exhilirated faces, hilarious interactions, and unstoppable amounts of radiant joy I was watching only led me to one conclusion:

This weekend was too damn good to only happen once.

But even if other forces decide to conspire against it, the fact that Flatine Fest happened the way it did—flawlessly smooth, endlessly enjoyable, and full of more talent than anything like it—is a living testament to the absolute legends that fuel the Denver metal scene. Here’s to hoping this isn’t the last time Dave Otero and Chelsea Lowe decide to throw a party with 700 friends.