Applause rippled through the audience as Phish took the stage and wasted no time launching into its first song, “Walls of the Cave” from the 2002 album “Round Room.” Starting off slow, the ballad grew more feverish as lead singer Trey Anastasio broke into a guitar solo, the start of a prolonged jam that worked concertgoers into a steady, pulsing groove.

The first set of the two-day Phish festival brought with it the surreal, carnival-like atmosphere that has become a hallmark of the band’s live shows. Fans got a bird’s eye view of the show atop a Ferris wheel, while a stand of upside-down trees stood guard in the far reaches of what concert organizers call “the back forty” _ the hills in front of the concert stage. Silver-colored sculptures dotted other parts of the venue, and fans flew kites of varied color and shape near dividers painted to resemble a massive picket fence.

Phish played three sets a day until the band’s final gig late Sunday night.

Saturday’s concert marked the culmination of a day that saw Vermont State Police set up roadblocks to turn away traffic because of muddy conditions inside the festival venue, a 600-acre state airport in northeastern Vermont. Organizers said fans who were denied admittance would be refunded.

But the promise of a refund was no comfort to fans stopped on Interstate 91 Saturday, many of whom abandoned their vehicles and headed out on foot for the concert site, about a dozen miles from the nearest exit.

“There is no way I am not going to try to get in,” said Erika Sander of Blodgett, Oregon, who left her rented car on the interstate to walk to the show. “There’s no way I’m going to be defeated.”

State police said Saturday afternoon that between 2,100 and 2,500 cars had been abandoned on the interstate, and that some 6,000 people had walked from the highway to the concert site. At a news conference earlier in the day state police Sgt. Bruce Melendy said he was not prepared to say how many fans were gathered inside the state airport. Estimates he provided on Friday tagged the size of the crowd at around 23,000.

With a following of thousands, Phish has become a latter-day Grateful Dead, a band celebrated as much for its music as for the community that has evolved over the jam band’s two decade-long history. Many devotees have based their lives around the band’s touring schedule, and it was clear that fans at this week’s festival were able to endure days of rain, mud and waiting in traffic just to see Phish play live.

“I would totally do it again,” said Rachael Gitlitz, 26, of Manchester, N.H., as she sat with a friend before the concert. “I’m really excited for the band to start.”