SACO — Stepping onto the Downeaster train line’s dome car is a little like going back in time.

The upper level of the passenger car contains a lounge with padded swivel chairs, tables and benches, all encased in a glass dome that gives riders a 360-degree view of the scenery as the train travels between Portland and Boston.

It’s a unique experience, and one that local passengers may not be able to repeat. The dome car is running on four daily Downeaster trips between Portland and Boston until Sept. 18.

This is the first time Amtrak’s 70-year-old Great Dome car has been used on the Downeaster line, and the first time a dome car of any kind has been used for revenue service in New England, said Patricia Quinn, executive director of the Northern New England Passenger Rail Authority, the agency that operates the Downeaster service.

On a short trip between Saco and Portland last week, about a dozen passengers sat around the lounge, taking in the sights.

Sitting near the front of the car, Kerstin Egenhofer was reading a book and occasionally gazing out the window. After taking time off work in Boston, Egenhofer was treating herself to a day trip to Portland, and had decided on a whim to take the train instead of the bus. She didn’t know about the dome car and couldn’t remember the last time she’d been on a train. But once she found the staircase to the dome compartment, it was hard to tear away.

“I wanted to make an experience out of my trip,” Egenhofer said. “This put the bow on it.”

From inside the curved windows, passengers watched the scenery roll by, passing the Scarborough Marsh and the Nonesuch River and busy Grand Avenue in Old Orchard Beach. The observation car also passed through a disused mill complex in Biddeford, the sprawling Rigby Yard railroad terminal in South Portland and the exercise grounds of the Cumberland County Jail in Portland.

Viewed from the curved windows of the dome car, even those vistas were attractive to Egenhofer.

“It’s a forced perspective shift,” Egenhofer said. “Even the ugly, industrial stuff I drive by going from Boston to Maine has a certain charm.”

The interior of the 70-year-old dome car contains a lounge with padded swivel chairs, tables and benches, all encased in a glass dome that gives riders a 360-degree view of the scenery. as the train travels between Portland and Boston. Brianna Soukup/Staff Photographer

The dome car was built in 1955 and is the only one of its kind in the Amtrak fleet. It has an annual route along the Adirondack Mountains between Albany, New York, and Montreal during the fall foliage season, but other movements are at the discretion of Amtrak’s president. The Downeaster requested a turn with the dome car in a bid to give frequent riders a new experience and draw in those who haven’t tried the Downeaster yet.

“We are always looking for opportunities to improve customer service and offer something new and different for our passengers,” Quinn said.

Somewhat ironically, the search for more passengers is what kicked off the dome car trend about 70 years ago.

The first dome car was built in 1945 and was attached to a daytime train that ran between Omaha, Nebraska, and Chicago, said Richard Luckin, a documentary filmmaker who produced “Dome Car Magic: A History of Railroad Dome Cars” in 2006 for the PBS television network.

Amtrak’s dome car, with the red, white and blue markings, is first in the line of passenger cars as the Downeaster travels through the Scarborough Marsh. The dome car hasn’t been used on the Downeaster line before. Photo by Bill Lord/Maine HDTV

In 1947, General Motors teamed up with the Pullman-Standard rail manufacturing company to build the Train of Tomorrow, which featured four dome cars, Luckin said. That kicked off a trend among private passenger rail companies that wanted to innovate and improve transportation, he said.

“It was just a way for railroads to ignite passenger rail travel after the second World War,” Luckin said. “It was really to offer something new.”

More than 200 dome cars were produced and ran on lines mainly west of Chicago, the West Coast and the Southwest. The last dome cars were built in the late 1950s. When Amtrak took over U.S. passenger rail service in 1970, it replaced most of the secondhand, high-mileage dome cars, said Amtrak spokesman Mike Tolbert. Others were retired in the late 1970s when the company introduced head-end power locomotives, Tolbert said.

Some of Amtrak’s routes west of Chicago have second-story observation cars, and Via, Canada’s national passenger rail company, runs Ultra Dome cars built by a Colorado company until about 10 years ago. Private rail companies also offer services with refurbished dome cars.

But because of height restrictions, train passengers on the East Coast never really had the chance to experience dome cars, and still only get sporadic opportunities to try one out.

The current run of the dome car might be the last chance Downeaster passengers have to ride in it. Depending on its performance this year, the Downeaster may or may not request the car again next year, Quinn said.

Seats can’t be reserved, and there is no extra fee for riding in the dome car.

On a trip last week, Susan and Glen Kerkian were taking the train from Durham, New Hampshire, to spend a couple of nights in Portland before riding the rails down to Providence, Rhode Island. The couple took an Amtrak train from Ohio to the East Coast for their honeymoon and ride passenger trains as much as they can. Glen Kerkian said he especially likes the unique views he gets from a train seat.

“It’s all the back way,” Kerkian said, watching the landscape fly by the domed windows. “Some of the views you see are spectacular; you’d never get them from the interstate. It’s a whole different perspective.”