What was once a bike shop and would soon become an apartment complex was the site of a party straight out of hip Bostonians’ dreams on Monday.

Under a punishing Labor Day sun, PA speakers blasted out performances from local musicians, vintage T-shirts swapped hands and $2 Pabst Blue Ribbon flowed by the cupful.

It was a free outdoor neighborhood block party and the grand opening for POP Allston, a temporary pop-up space on Brighton Ave. that houses a free indoor skate park, DIY bike shop and community space. Boston’s Mayor Marty Walsh announced the space’s launch in June. It will stay there until developers begin converting it to 138 units of transit-oriented housing.

For now, partygoers said, the multi-use building and parking lot could be the next big thing in the neighborhood, home to thousands of Boston’s college kids and twenty-somethings.

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“If this is accessible and anybody with a good idea and a budget can get it, this would be the perfect performance space for summers,” said Michael Christmas, a local rapper and onetime Allston resident, just after his set on the block party’s outdoor stage for a crowd of 200 or so.

In Boston, he said, it can be hard for up-and-coming artists to find medium-size spaces that will let them perform. POP Allston could be an exception, the artist told Metro.

“I could see a lot of shows for local artists here, and I’ll go to all of them,” he said. “It just needs to be accessible.”

The party was also a tribute to Allston Christmas, the city’s big annual day for young renters to move in and out of apartments. So it featured a red, white and blue (PBR-sponsored) plastic holiday tree and a “Merry Allston Christmas” mural painted on a brick wall outside. The complimentary “bicycle valet” booth, sponsored by the CommonWheels Bicycle Collective, was decked out with stockings and ornaments.

Just about everyone who spoke to Metro lived in Allston and had just moved.

“It’s a nice in-between from moving in and going back to school,” said Lauren Mahoney, an Allston resident and senior at Lesley College.

Others mourned the loss of International Bicycle Center, a staple for local cyclists, which sold the building on Brighton Avenue earlier this year.

“It was sad to see International Bicycle go,” said Davin Surin, who grew up in the neighborhood. “I’m not sure what it’s going to become, but it’s a great location and I hope it gets used properly.”

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Inside the new indoor space, Sam Kleiman was selling vintage T-shirts – a lot of them, he told Metro, though he declined to give specifics. He said he usually sells shirts, ranging from $15 to more than $500 (for a rare Sex Pistols T), on Sundays at the SoWa Open Market in the South End, but said he was looking forward to reaching a new audience.

“I’m happy to be part of it from the very beginning and kicking off the space,” said Kleiman, who also promotes his shirts on Instagram (@bowiecokemirror). “This is a great opportunity for me.”