Tens of thousands of fans screamed and danced Saturday in a fantasyscape of upside-down trees and silver sculptures for the first in a series of farewell concerts by the jam band Phish (search).

Applause rippled through the audience as the band launched into its first song, "Walls of the Cave" from the 2002 album "Round Room (search)."

Starting off slow, the ballad grew more feverish as lead singer Trey Anastasio (search) 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 festival brought with it the surreal, carnival-like atmosphere that has become a hallmark of the band's live performances.

Fans could get a bird's-eye view of the show atop a Ferris wheel. A grove of upside-down trees stood in the far reaches of what concert organizers called "the back 40" — the hills in front of the stage.

Silver-colored sculptures dotted other parts of the venue, and fans flew kites near dividers painted to resemble a massive picket fence.

Phish is scheduled to play three sets a day until the band's final gig late Sunday night.

Vermont State Police set up roadblocks to turn away traffic because of muddy conditions inside the venue, a 600-acre state airport in northeastern Vermont. Organizers said fans who were denied admittance would receive refunds.

But the promise of a refund was no comfort to fans stopped on Interstate 91, many of whom abandoned their vehicles and headed 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, Ore., who left her rental car on the highway.

As many as 2,500 cars had been abandoned and some 6,000 people had walked from the highway to the concert, police said.

Sgt. Bruce Melendy declined to estimate how many fans were gathered at the airport. On Friday, officials said the crowd numbered about 23,000.

During its two-decade history, Phish has become a latter-day Grateful Dead, a band celebrated as much for its music as for the community of loyalists who follow the group.

Many devotees based their lives around the band's touring schedule. Fans at this week's festival endured days of rain and mud while waiting for the final concerts.

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