It’s one of his favorite days of the year to get out and rock, but David Doherty of Minneapolis decided Saturday’s Rock the Garden festival was also a good day to head inside Walker Art Center for some modern art. Too bad the galleries were actually closed up for the day.

“I guess they don’t trust the rock fans with the priceless art,” said Doherty, who still loitered in the museum during the 17th installment of its almost-annual music fest enjoying his ulterior motive.

“Air-conditioning might be better than art today anyway.”

Despite the festival-dictated closure of the galleries — which RTG ironically serves to promote — many of the event’s 11,000-plus attendees not surprisingly took advantage of the cooler conditions inside the Walker amid Saturday’s humid 90-plus-degree afternoon heat.

The weather did not dampen attendance, thanks to anticipation for headlining band the National’s first Twin Cities set in six years. However, the scene was unusually chill on the hillside next to the museum as only a modest crowd welcomed the doubly heated opening set by St. Paul rapper Dem Atlas, followed by local scenemaker Har Mar Superstar’s flirty new electro-pop duo Heart Bones.

“My shirt is made out of a towel, so we’ll see how it goes,” Sean “Har Mar” Tillmann said after taking the stage in a vintage, terry cotton-style T-shirt to match his group’s ’80s flavor.

Tillmann and his co-vocalist Sabrina Ellis deserved some kind of MVP award for going through all their Wham!-like excited dance motions despite the sweltering heat. Then again, rock acts don’t come much more resilient than the band that followed Heart Bones to the main stage: legendary Los Angeles punk band X.

“What a beautiful park and a beautiful city,” singer Exene Cervenka raved a few songs into her band’s impressively hard-throttling 50-minute set, not complaining once about the weather.

She and her 60s-aged bandmates tore such riotous staples as “White Girl” and “Hungry Wolf” but also coolly slowed down for the doo-woppy “Come Back to Me.” In the latter, cancer-surviving guitarist Billy Zoom delivered a lengthy sax solo with his guitar pick stuck to his forehead — the sweat helping him make sure he didn’t lose it.

While X fit in well as a veteran act for the RTG main stage, the smaller stage inside the Sculpture Garden served up a couple noteworthy newcomer acts. New Zealand pop-punk quartet the Beths earned a rave response there with its ultra-catchy, wryly written Lemonheads-meets-Rilo Kiley pop-punk tunes.

Maybe the first performer to crowd-surf off the garden stage — or certainly the first to do it while quoting Sylvia Plath — bluesy South Carolinian singer/songwriter Adia Victoria then dedicated her haunting epic “Heathen” to women battling for reproductive rights in Alabama.

Under the setting but still simmering sun, fans fully crammed the hillside for the final two main stage sets by Australia indie-rocker Courtney Barnett and her summer tourmates, the National.

Barnett and her backing duo started off with her slow-grooving breakout hit “Avant Gardener” and gradually built to several Nirvana-like, small-scale/big-noise blowouts with “Nameless, Faceless” and the finale “Pedestrian at Best.”

A Cincinnati-bred rock quintet with classically tinged sonic forays and artfully dissonant lyrics, the National marked another less-than-summery headliner for the summer music fest, whose lineup is based heavily on co-organizer 89.3 the Current’s playlists. Like pal Bon Iver did at RTG 2017, though, the National put on a much more vibrant and musically ornate stage show Saturday than its records suggest.

The added touches of electric elegance were apparent right away in opening songs “You Had Your Soul” and “Quiet Light,” each from the group’s latest album and prominently featuring guest singers Zoë Randell and Pauline de Lassus (the latter guitarist Bryce Dessner’s wife). Another new one, “Where Is Her Head,” was turned way up into a manic, upward spiraling triumph.

The band’s full-time singer Matt Berninger showed off his unique charm later in the set, bellowing out the deep melody in “Don’t Swallow the Cap” and matching the percussive drive of “Graceless” with total grace. In the end, the weather cooled off but the crowd was as hot for the National as any RTG headliner of recent memory.