On a sunny summer afternoon, about 25 men and women — ranging from millennial to baby boomer — gathered on Cambridge Street for the “1970s counterculture walking tour” of Inman Square.

The tour's leader, Tim Devin, lives in Somerville and has become something of an unexpected expert on the Boston-area counterculture of the 1970s. He's a librarian by trade, so he’s no stranger to the joys of the research rabbit hole.

"The last few years I’ve been looking at 1970s Boston counterculture," he said, "looking through old books and old magazines, and just learning about what people were doing and where they were doing it and why they were doing it."

The more he uncovered, the more he was inspired to dig deeper. The deeper he dug, the more he said he was surprised by the range and scale of Boston's counterculture.

"In Cambridge, for instance, there were over 100 groups, which seemed like a lot to me," he explained. "There were these subcultures in, like, Inman Square and Union Square that kind of supported each other and fed off each other. So, I thought that was kinda interesting, so I started mapping them."

Devin compiled his maps and research into a series of publications — appropriately DIY, zine-like pamphlets titled "Mapping Out Utopia" —that cataloged who these many groups were, what they did, and where and when they did it. But true to the spirit of the era, he wanted to take what he learned to the streets, and so he began organizing these walking tours.

"It’s an interesting way to view history," said Devin. "History can be super dry if you’re reading a history book. But if it’s in a place where you live or that you’re familiar with, and you see the actual building where this thing actually happened, it makes it more accessible."

Devin uses “counterculture” as an umbrella term for a panoply of people and groups — from feminists to civil rights activists, alternative-lifestyle hippies to political revolutionaries, cooperative businesses to underground publishers.

As Devin led the group through the neighborhood, he pointed out the buildings and spaces — most pricey residential spaces today — that were once home to feminist organizations like The Women's Law Collective, activist groups like the Non-Violent Direct Action Training Collective, art cooperatives like The People's Gallery, environmental groups like Boston Area Ecology Action, and Trout Fishing in America.

"Trout Fishing in America was an alternative school," said Devin during the tour. "The idea was: $10 a month towards a GED, you studied whatever you wanted and you had a say in the way the structure was run."

Today the space is a 7-unit condo complex worth more than $5 million.

We ambled past 186½ Hampshire Street, today a therapist's office, home in the mid-1970s to the Massachusetts Feminist Federal Credit Union.

"Women couldn’t get loans unless they were married and their husbands co-signed, which just seems so bizarre now, but it was true," said Devin.

A little further down was 134 Hampshire Street, presently Oleana Restaurant, which was once Bread and Roses restaurant, an entirely women-owned and -operated cooperative eatery.

"After a couple years half of the group wanted to make it closed to men entirely," said Devin. "The other half didn’t like that idea. They split, and they renamed the restaurant the Amaranth."

Some of these groups evolved into organizations that are still around today. Most lasted a few years, many just a few months. Still, said Devin, each of them deserves to be remembered.

"It laid the groundwork for a lot of the things we have today like local food, a lot of advances that feminism made," he said. "We owe a lot to the '60s and '70s counterculture."

That’s something that came as no surprise to some folks on the tour, like Susanna Bolle, who said she spent plenty of time in Cambridge back in the 1970s.

"I’m always really interested in the changing use of space in the city," she said, "the flux and history of space."

But for others, like student and Ohio native Alula Hunsen, the brief living-history was a total revelation.

"I had no idea that this area had such a history of radical feminism and community organizing, collectives and alternative economies," he said. "That’s something I am studying as part of my research at MIT."

Still others, like Olivia Bornstein, came out looking for insight into a lifestyle that she said still resonates with her and many of her friends.

"I was curious, like, what’s been done before [and] why it ended," she said. "You can Google stuff, but going on a tour like this is so much more personal and informative."

And if you want to experience the tour in person, you still can. Devin will hold one last, free 1970s counterculture walking tour of Cambridge this fall before he turns his attention to whatever rabbit hole he falls down next.