More than eight million people call the 302-square-mile landmass containing the five boroughs of New York City home, making it the most densely-populated urban area in the United States. Were NYC a state, it would rank ahead of Virginia (42,774.2 square miles) as the 12th most populous one in the union. For that reason and many other issues that arise when many bodies are crammed into tight spaces—cars, pollution, endless roads, etc.—it is not, one might think, a great place to be an ultramarathoner. One would also be wrong.

Gotham's ultrarunning scene has existed since the sport's early days in the 1960s and '70s, and it's exploded in popularity over the past half-decade or so. Running along the Manhattan streets with a backpack while devouring a packet of goo is the new skinny black jeans—and it’s not that surprising when you think about it. In many ways, it takes the same kind of person to enjoy endless hour-on-hour runs as it does to survive the perpetual craziness that is living in New York.

"We have so many challenges day-to-day: getting a job, an apartment, a parking space. You're always competing—not vocally but internally—just to sustain life," says Rich Innamorato, the founder of the Broadway Ultra Society and an ultra-race director for over 30 years. "Ultras are like that, too. It's a private challenge. You're not pounding your chest saying 'look what I'm doing,' but you're doing it."

Despite the city's deserved reputation as a concrete jungle, there are plenty of places to run. The park systems connect, especially in the outer boroughs. There's the Westside Highway and the Waterfront Greenway in Manhattan; the bike path along Pelham Parkway to Orchard Beach and City Island; the Vanderbilt Motorway that goes out to Flushing Meadows; a bike path on the Cross Island Parkway and one on the Saw Mill Parkway; the bridges in Far Rockaway; the Williamsburg/Manhattan/Brooklyn Bridge trifecta. Point being: if you look, you will find a way to run forever.

This summer, Phil McCarthy, who broke a record by running 257 miles during a 48-hour span in May 2011, did just that. He created and organized a 100-mile race around NYC. "I thought it would be a really good way to show off the different places in the city,” he says. “The parks, greenways, boardwalks, and bridges." Thirty-one runners started and 14 finished the Great New York 100 Mile Running Exposition, which Keila Merino won in 21:05:55. Michael Samuels, the first male finisher, followed four minutes later. Next year, McCarthy hopes to do it again and expand the field. He'll have plenty of interested participants.

One of the runners might be Deanna Culbreath, who volunteered to help coordinate McCarthy's race in July. The 32-year-old is an up-and-coming talent in the ultrarunning world. Unlike many other runners who track everything, she doesn't meticulously plan. She leaves her apartment on the Upper East Side and, well, "I usually just make up a lot of my long runs. I don't know where I'm going to go. I just go out for four hours. Whatever. Who cares?"

And while “young woman training for race by running through New York at night” sounds like the start of a really bad slasher film, it hasn’t stopped her. "I'll start a run at two in the morning during the work week, then go straight to work,” Culbreth says. “It works out so well mentally. It gets you ready for those long dark hours of a 100-miler when you're out there by yourself."

In fact, New York may be one of the safer places to exercise outdoors, whatever the time. Culbreath and her fellow ultras can almost always run with other people. The presence of so many warm bodies in a condensed area makes it tough to find a time when no one can go for a jog. Websites like Facebook and Meet Up make locating like-minded individuals with the same schedule even easier. Plus, many places in New York are well-lit 24 hours a day. The city can be a dangerous place at 3 a.m., but it's not so bad when you know where you’re going.