About 100 little tykes in pajamas boarded the trolley at Lake Harriet last week for a "PJ Party" that sold out in six minutes. This weekend, an older crowd is helping solve "A Most Modern Murder" mystery on the historic streetcar. Then some lucky children will go to streetcar camp and learn to operate a 100-year-old trolley.

Each year about 40,000 visitors board the historic trolleys at Lake Harriet and downtown Excelsior to participate in special events or just ride the rails. They're part of the changing face of the Minnesota Streetcar Museum, a mobile museum that takes frugality — and patience — to new heights.

Next year marks the 60th anniversary since streetcars were pulled off Twin Cities streets, trolleys that once carried more than 200 million passengers a year. Most were stripped and burned.

But one trolley was donated intact to the railway fan club, and that evolved into the Streetcar Museum. Juggling the preservation of that rare gem and others since discovered, while attracting 21st century fans, is the museum's challenge.

"Like all railway museums, we're doing what we can to bring people in and introduce them to our work," said Rod Eaton, the museum's general superintendent. "Our mission is to make streetcars come to life for the next generation."

The museum occupies an unusual niche among nonprofits. It has no building. It has no paid staff. No offices. No glitzy galas or golf tournaments.

It spends less than $100,000 a year to operate the trolleys, host special events, and painstakingly restore some of the state's few remaining streetcars, said Eaton.

The museum chugs forward thanks to more than 200 volunteers, including conductors and a group of retirees who think nothing of spending seven years restoring a trolley, bolt by bolt. Those volunteers are gearing up for the final push of summer programming.

"We keep our expenses really low," said Jim Vaitkunas, a volunteer who is secretary of the board of directors, a streetcar conductor, newsletter editor, and in-house insurance policy coordinator.

"We have no paid staff. Our bookkeeping is done by a volunteer accountant. And we only restore one streetcar at a time. And it takes six to 10 years, so we spread out the financial hurt."

Jon Pratt, executive director of the Minnesota Council of Nonprofits, calls the museum an example of nonprofits sustained by "super volunteers."

"A group like this shows the amazing power of volunteers, whose work is equal to money," said Pratt.

Old trolleys, new traditions

That lone streetcar donated 60 years ago now operates on a one-mile track along Lake Harriet. It is joined by restored streetcars from Duluth, Winona and another from Minneapolis. In Excelsior, a Minneapolis and a Duluth streetcar take passengers.

The trolleys are creating memories for modern families.

"When I was 5, we'd come here from South Dakota to visit my great-aunt," said Mike Fuller, of Golden Valley, taking a photo of his young daughters on the trolley last week. "Now we come here for my daughters' birthdays. It's carrying on the tradition."

Sonia and Jim Casey, also of Golden Valley, were boarding the trolley with their two young sons.

"It's a piece of history," said Sonia Casey. "There's the LRT [light-rail transit] now. They can see what we had before, and what we have now."

While the Caseys and Fullers are regulars, the museum has to dream up ways to attract others to the rails. Enter the growing list of special events — all with a link to history.

The mystery theater this weekend, for example, is set in 1954, the year that the trolley system ended, said Eaton.

The pajama parties hearken to the days when mothers would board the streetcars on hot nights with fussy children. The trolley's rumble and the cool breeze would lull them to sleep.

Special events now account for 30 percent of the museum's revenue, said Vaitkunas. Meanwhile, trolley rentals, which go for $75 for a half-hour, have taken off this year, said Eaton.

"Last week we had two birthday parties and a wedding," said Marv Krafve, a retired engineer from Plymouth. "We've got 53 senior citizens coming today."

10,000 hours later

Twice a week, about 10 retirees like Krafve head to the "car barn," where volunteers spend more than 10,000 hours reviving streetcars. Most had been converted into funky cabins before being given to the museum.

They strip the cars down and rebuild from the skeleton. On this day, some were working on a sliding passenger door.

"This door and its mechanisms required more than 1,000 parts," said Ken Albrecht, a retired engineer from Mankato who oversees the work.

Finding the parts to old trolleys can be like a national scavenger hunt. A newspaper article might trigger a call. Railway museums share their loot. Folks at trade conferences offer tips. If worse comes to worst, they make the part themselves.

Albrecht estimates he puts in 20 hours a week and 15,000 miles a year on the trolley. He also grows about 400 pumpkins to give away at Halloween special events.

These older mega volunteers are both the strength and the weakness of the organization. While the museum has recruited younger volunteers to operate the trolleys, run the Facebook and Twitter pages, and operate some special events, getting a long-term commitment is much harder, said Eaton. And that is the museum's real challenge for the future.

"You can do a lot without money," said Eaton. "But you can't do a lot without good people."