Sebastian O'Kelly, left, and Brad Kennedy, both of Bethesda, consult their map during a hike from McLean to Tysons Corner. The two have set themselves a challenge: to hike around the whole Beltway. (John Kelly/The Washington Post)

Just when it seems that every new land has been discovered, every mountain climbed, every river crossed and every jungle penetrated — just when it seems there are no new adventures left — here come Sebastian O’Kelly and Brad Kennedy. Their audacious plan: to hike the entire circumference of the Capital Beltway.

But first, they need to look at their phones.

“This is what I was looking at,” says Sebastian, pointing out a squiggle on the map on his phone. “It looks like a trail. It may not be real.”

We’re standing in the parking lot of the Langley School in McLean, Va., on a recent weekday afternoon. Sebastian and Brad are doing their 64-mile Beltway hike in stages, two to four miles at a time, and this is where they ended their most recent leg.

The idea is to hew as closely as possible to the Beltway’s inner loop. We crowd around the phone as Sebastian notes streets and paths and what in Virginia they call “runs”: small streams whose banks may provide passage.

O’Kelly and Kennedy started in Bethesda and are tackling their trek in legs, a few miles at a time. They are trying to hike on surface roads, paths and trails as close to the Beltway’s inner loop as they can. (John Kelly/The Washington Post)

He also notes that the National Counterterrorism Center is between us and the Beltway. “We’ll want to stay away from that,” he says.

And then we’re off, down Balls Hill Road, across Dolley Madison, right on Chain Bridge Road, working our way ever closer to the great, multilane ouroboros that is I-495, an asphalt snake swallowing its tail. And why are we doing this, exactly?

“I listen to one of these podcasts, ‘The Art of Manliness,’ ” explains Sebastian, 52. “It isn’t quite what it sounds like. It’s a guy who does podcasts on what it means to be a 21st-century man.”

One of the guests was an honest-to-goodness adventurer, an English bloke who had sailed oceans and bicycled continents. Such feats may be beyond most of us, he’d said, but anyone could embark on a “micro-adventure.”

Sebastian wondered what his micro-adventure might be. He happened to be stuck in Beltway traffic on the way to his office in Reston, Va., a familiar fate for any commuter who depends on the sclerotic highway.

He invited his friend Brad to partake — their kids go to school together — and in April they set off for the first time from their Bethesda neighborhood. They hope to finish in 12 months.

Brad, 46, says his kids consider his adventure “weird Dad stuff.” Sebastian blogs about it at beltwayhike.com.

The two men were enchanted by the idea of “micro-adventuring,” their own version of across-the-globe bushwhacking. Their journey has taken them over hill, over dale and even through the Potomac. (John Kelly/The Washington Post)

We pass a water tower that’s set back from Chain Bridge Road. The entire hillscape is engulfed in drifts of choking kudzu. Sebastian says, “If we went into that middle of that, we might not get out. It really is no joke.”

He’s forgotten his machete today, but he usually brings one. Brad says, “I think Sebastian was hoping to bushwhack the whole thing.”

That’s not necessary here, as we’re on a sidewalk, ambling past new residential high-rises designed to capitalize on a more “walkable” Tysons Corner. We pass under thetracks of the Silver Line and walk up Scotts Crossing Road until it dead-ends. On our right are the Gates of McLean condos. To the left is a vast construction site. Ahead: a tall, gray sound wall stretching in either direction atop a weed-covered embankment. We could turn around, or. . . .

We scramble up the hill and walk through the thigh-high scrub, the Capital One building on our left, the guardrail on our right. Traffic zips by yards away. The Beltway is actually moving today.

Perhaps you saw us that evening: three men, purposefully striding, conquistadors of concrete.

After a hundred yards or so, Sebastian peels off and scrambles down the hill, through a tiny wood and over a sagging fence. Brad and I continue to the on-ramp for Route 123 and hang a left. Our two parties — modern-day Lewis and Clark — meet up near the Capital One parking garage and press on.

We’re in an office park on Old Meadow Road when the heavens open. We wait out the storm under the overhang of a nondescript building.

The pair of Beltway adventurers have quintessential Washington jobs: Sebastian is a lobbyist, Brad a lawyer who does corporate litigation. Sebastian drives the Beltway nearly every day. Brad works downtown, so he doesn’t. They tell me a highlight of their adventure so far was swimming the Potomac in the shadow of the American Legion Bridge.

Wasn’t that risky? I ask. No, they insist. The water was shallow and calm that day.

“I think it’s more dangerous crossing it in a car,” Sebastian says.

“The fun thing is, you go from these really urban environments to these very natural environments,” Brad says of their expedition.

They’ve seen deer, herons, groundhogs and countless squirrels. They’ve seen the worn dirt and flattened grass of game trails and the abandoned tents of homeless men.

After 45 minutes, the rain stops and we go looking for Scott’s Run. On the map it appears to travel under the Beltway, meaning we might be able to walk it and emerge in Tysons Corner. Not today. We find what must be the stream: a culvert afroth with raging storm water runoff.

“If there was four inches of water, we could do it,” Sebastian says. “But there’s two feet in there.”

Two hours after we set off, we arrive at the Westin Tysons Corner off Route 7. Brad orders an Uber.

“These guys are walking around the Beltway,” I tell the driver once we get in.

He laughs, unsure of whether I’m joking, and takes us back to our cars.

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/johnkelly.