Walter Barrera is seen at the end of a 20-mile training run in Northeast Washington in this file photo. (Michael S. Williamson/The Washington Post)

D.C. is full of runners: road runners, ultramarathoners, adventure racers, and more. And they’ve all got a story, a special run and a favorite trail.

Frank Fumich started running when he turned 30, the year his aunt was dying of brain cancer.

“I thought it would be neat to run the Marine Corps Marathon and offer it up for her while she was suffering from cancer,” said Fumich.

That first race “hurt like hell,” he says now.

Fumich hasn’t really stopped running — or paddling, or trekking, or anything else — ever since.

On a recent July afternoon, he headed out on one of his favorite trails for a short seven-miler. He wore a gray shirt, an ID bracelet, UnderArmor shorts, and a pair of bright green-yellow Hoka running sneakers that looked like a pair of foot-size inflatable mattresses.

He took off on a short grassy section before dipping into the body of the trail, bouncing over plank bridges, scrambling over rocky outcroppings and along paths carving through small hillocks along the Potomac Heritage Trail, which follows the Potomac from Roosevelt Island northwest along the Virginia side of the river.

“There are very few people out there,” he said. “Even on a beautiful, sunny day, you can be out there and feel out on a far-out trail and you’re just a mile from a massive city.”

“And it’s nice to see the river,” he said.

After a sweltering June and July, the air is crisp, the river an intense blue, broken up by the occasional scull or kayak.

“I just wanted to keep pushing the envelope,” Fumich said of his running. He ended up competing in a slew of Ironmans and adventure races, paddling more than 30 miles of open water and participating in the 41-hour, cringe-inducing “Death Race Challenge” in Vermont. Most recently, he ran from D.C. to Boston in solidarity with the victims of the Boston Marathon bombing.

The Potomac Heritage Trail is just one of the dozens of trails around D.C. region that runners and racers can use to get off pavement and into relative solitude in nature, local running experts say. On Fumich’s run, he passed four or five runners and two fishermen.

Jim Harman, founder of EX-2, an adventure racing company that sponsors dozens of races in the D.C. area every year, said that one of his favorite runs is at Fountainhead Regional Park in Fairfax Station, 20 miles southwest of Washington.

“It’s just awesome,” he said. “For being right in Fairfax County, not many people know about it. It has a very remote feel on the trails . . . but it’s just great place to run. It’s technical, challenging, beautiful.”

“Just from an access point of view, there are a lot of great trails in the area,” said Mike Acuna, director of the Parks’ Half Marathon, which takes place in September and takes runners through Montgomery County’s parks from Rockville to Bethesda.

“In this area it’s hard not to find a scenic place to run,” he said, ticking off trails such as the Capital-Crescent trail or the C&O Towpath.

In D.C., runners can run along the mall, or through Rock Creek Park, or even along Fort Dupont.

In Virginia, there are trails such as the Potomac Heritage Trail and the Mt. Vernon Trail. In Montgomery County, there are miles and miles of trail networks along the Potomac River and through the county’s forests and parks, according to Karen Kincer, president of Montgomery County Road Runners, one of the region’s largest running clubs.

Kincer doesn’t participate in any of Fumich’s crazy quintuple Ironmans, but she routinely runs 20-milers in and around D.C.

“Washington has a lot of type-A personalities — people with very involved careers,” she said. Running offers an immediate, daily sense of accomplishment that people can easily fit into their schedules, she said.

“It’s not like going to the gym, or to team practice,” she said. “You can get your sneakers out and run anywhere.”

Clubs like the Montgomery County Road Runners offer support and motivation, as well as a social component, she said.

“What’s really great about it, it’s my time. No one else is dictating what I’m going to do. It’s this freedom, it’s all about me and my running partners,” Kincer said.

And it keeps runners motivated.

“Leaving someone on a street corner at 5 a.m. is really rude!” she said, with a laugh. “People holding you accountable to be somewhere — that keeps you on your toes. It keeps you going in a very low-key way.”