In a spectacular yearlong event, the National Geographic Channel series America’s National Parks will show you the parks’ natural wonders—both big and small—as you have never experienced them before.

There is magic here, the delight in being not quite lost and not quite found.

I am off trail, following an unnamed stream in northeast Ohio, scrambling over downed trees through a ravine of crumbling shale, the water milky with silt as it cascades over tiny falls. The sun dances with the stream and the hardwoods. When I take off my boots and splash in the small pools, I feel the cool of the mud between my toes. In the distance, just over the rise, the sound of the city comes and goes. Civilization is so close and seems so far, and in that toggle is the wonder of an urban park.

The place is an offshoot of Cuyahoga Valley National Park, which stretches like a skinny inkblot between the gridded sprawl of Cleveland and Akron. The park’s centerpiece is the resilient Cuyahoga River, once a punch line about environmental ruin after an oil-slicked pile of debris on the water caught fire. The park came five years later, in 1974, first mostly in name, and then slowly assembled from land across the compact valley.

View Images Commuters listen to a band on a pedestrian bridge spanning the Cheonggyecheon park in Seoul, South Korea. The stream, although important to the city’s culture and development, was intermittent, dwindling to a rivulet at times. To ensure a constant flow, more than 30 million gallons of water is pumped in daily from the nearby Han River. Most residents view that artificiality as an acceptable trade-off for the serenity the park brings to the city.

The grandeur is varied and comes in small doses. Sandstone cliffs are hidden in the woods. A former auto repair yard is now a marsh created by beavers damming an old canal. And on the site of an arena that was once home to the Cleveland Cavaliers basketball team, there is a broad field that’s ideal for watching hawks. The built and natural worlds are in proximity, layered and competing for attention from the bikers and hikers and joggers making their ways up and down the old canal towpath.

This is the urban park of today. Unlike the neatly drawn public spaces of an earlier age, these parks are reclaimed from the discarded parcels of our cities: Stranded patches of woods, abandoned military bases and airports, storm-water systems, rail lines and bridges, places where scraps of land are pieced together like quilts or strung together like beads.

The experimentation is global. Rail parks, many inspired by the success of New York City’s High Line, are now beguiling fixtures in Sydney, Helsinki, and other cities. Singapore is building an artificial rain forest inside Changi Airport. At the edge of Mexico City, an immense park is planned on what remains of Lake Texcoco.

I am captivated by the breadth of innovation and energized by the passion people bring to these spaces. As I explored them, what became clear is that urban parks aren’t a substitute for the enormous and often remote parks that protect our most majestic forests and mountains and canyons. They serve a different purpose; the truth is, we need both.

Immerse yourself in this quintessential urban oasis, smack in the middle of the city that never sleeps.

On a hot and hazy afternoon, I set off to walk the four-mile length of Cheonggyecheon, the lovely ribbon of water that unfurls with quiet assertiveness through the heart of Seoul.

In the city’s preindustrial years, the stream was where lovers courted and women gathered to do wash. But Seoul’s boom after the Korean War brought shantytowns and pollution, and the stream became an eyesore. In 1958 a road was built over it. An elevated highway, finished in 1976, completed the entombment.

There Cheonggyecheon might have stayed, if not for serendipity and politics. Throughout the 1990s, a small group that included academics and engineers sought to uncover the waterway. They figured out how to manage the stream’s hydrology and mitigate the traffic snarl that might ensue when the highway and the road below, which carried more than 170,000 vehicles a day, were removed. “I didn’t think the money was the problem,” said Noh Soo-hong, a professor of environmental engineering at Yonsei University and one of the project’s first supporters. “I thought it was the will.”

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View Images St. James's Park, London, England, opened in 1660 British soldiers march in the annual summer parade that marks the queen’s official birthday. The route runs through the park, which is adjacent to Buckingham Palace. Once a swamp, then the site of a hospital for patients with leprosy, the land became royal property in 1532, when Henry VIII acquired it as a preserve for deer hunting. When Charles II became king, he opened the grounds to Londoners, creating one of the earliest public parks. Rebecca Slater came with her church group to watch the event.

The missing component was a leader with clout. That person arrived in the form of Lee Myung-bak, a former construction executive whose company had been the principal contractor in building the highway. He made the stream’s restoration a key issue in his successful campaign for mayor of Seoul in 2002. (Five years later, he was elected president of South Korea.) “It was a very dangerous idea,” said Hwang Kee-yeon, a transportation engineer who helped develop the master plan. “Lee Myung-bak decided, ‘I built it. It’s time for me to demolish it.’ ”

Work on the $372 million project, a reclamation job of mammoth proportions, began in 2003. First the elevated highway was torn down. Then the surface road was ripped up, again exposing the stream. Like many restorations, this one is not entirely faithful to the past. The stream was intermittent, barely trickling in the dry months and surging during the summer monsoon. Thanks to pumping stations that deliver more than 30 million gallons a day from the Han River, the stream now babbles reliably.

“People criticize this as a man-made river or fish tank,” Lee In-keun, a wiry and animated man, told me as we strolled the upper portion of Cheonggyecheon. The paths by the stream were crowded with people enjoying the water and pointing with delight at carp idling in the deeper pools. Research shows it provides a cooling effect during Seoul’s steamy summers. Lee oversaw the restoration project and agrees that Cheonggyecheon is artificial. But that distinction doesn’t matter to him; he finds the presence of nature as vital as in a truly natural setting. “It’s a jewel of the city. You can hear the water flow in the central area of ten million people. It’s unbelievable. We made that intentional.”

View Images English Garden, Munich, Germany, opened in 1792 Summer attracts sunbathers, clothed and otherwise, to the grassy banks of the Schwabinger Bach. The meadows in this park, one of Europe’s largest, have been popular with nudists since the 1970s. Among its features are a Chinese pagoda, a Japanese teahouse, and two beer gardens with seats for 9,500. The park’s designer opted for a natural appearance rather than the more formal layout typical of parks at the time.

Cheonggyecheon begins in the financial district, within a canyon of office buildings. The stream flows east, the banks widen, the concrete gives way to thatches of reeds and glades of trees. It moves past glitzy shopping areas and tired-looking wholesale districts and gigantic apartment complexes that rise up like fortresses. At one point a pair of concrete abutments appears in the stream. Part of the old highway, they are reminders of the past and the impermanence of our engineering. Many Seoul residents find it hard to remember a time when the stream was covered, when herons didn’t wade gingerly in the water hunting for fish, when it wasn’t an inviting place.

I was near the end of Cheonggyecheon when I heard the singer. I followed her voice to a small stage under a bridge where a band was playing a Korean “trot” song, the honky-tonk sound mixing with haunting lyrics.

When I released my hold on my mother's hand and turned back,

Even an owl cried. So did I.

I sat on a stool at the edge of a gathering of retirees and listened, and eventually a woman with a sweet smile and a firm insistence asked me to dance. We shuffled to the music, holding hands, joined like the city and the park that runs through it.

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“This is where it all began,” said Amy Meyer, as we pulled into the driveway of Fort Miley, part of the Golden Gate National Recreation Area at the northwestern edge of San Francisco. A coyote stood in the middle of the road and stared at us, in no apparent hurry to move. Though the National Park Service has maintained a presence in cities for years (it oversees the National Mall in Washington, D.C., for example), the creation of Golden Gate is considered a turning point in the urban parks movement.

Meyer is now 82, and by turns gracious and feisty. In 1969 she was a stay-at-home mother when she heard about plans to build an archives center at Fort Miley, a largely empty coastal defense site a few blocks from her house. She began organizing to save the space as open land and eventually joined forces with activists on the other side of the Golden Gate Bridge who were alarmed that suburban sprawl might destroy the austere beauty of the Marin Headlands.

Golden Gate, along with Gateway National Recreation Area in New York and New Jersey, was established in 1972. These new parks signaled a move by the Park Service to look beyond its wilderness parks to more accessible places closer to America’s cities. As Walter Hickel, secretary of the interior and former governor of Alaska, said at the time, “We have got to bring the natural world back to the people, rather than have them live in an environment where everything is paved over with concrete.”

View Images Park Güell, Barcelona, Spain, opened in 1926 Designed by Antoni Gaudí as an exclusive neighborhood for Barcelona’s wealthy, the site failed as a real estate venture. The city bought the development and opened it to the public. Along the popular Dragon Stairway are mosaic sculptures, including a colorful salamander that has become the park’s unofficial mascot. Above the columns a large plaza offers sweeping views of the city and the Mediterranean Sea.

The people are definitely at Golden Gate, one of the most visited places in the national park system, drawing around 15 million visitors each year. It spans both sides of the entrance to San Francisco Bay, with miles of coastline, towering bluffs, redwoods, and remnants of former military installations. And there is an island, Alcatraz, where 4,000 tourists a day disembark from ferries to tour the former federal prison and ponder life behind bars.

The park can be nearly a circus, with locals on their morning strolls skirting past tourists, weekend Frisbee games and parties on the fields, and dogs on and off leash seemingly everywhere. Many visitors have no idea they’re in a national park. That’s understandable. There are no grand entrances. Adding to the confusion, San Francisco has its own Golden Gate Park, which abuts the national park near the ocean.

All this creates a daunting range of constituents, from hang gliders and politicians to surfers and commuters, and the battles over how best to manage the resources can be intense.

“We’re in a democracy, and democracies are messy,” Golden Gate Superintendent Chris Lehnertz said. A dog-management plan, for example, has been in the works for more than a dozen years.

Lehnertz also is working with area governments on a strategy for assisting the homeless, an issue at many urban parks. “I see a homeless person who spends the night here as a visitor,” she said, “just like I see somebody who walks their dog on a beautifully groomed trail.”

One morning I drove about five miles south of San Francisco out to Milagra Ridge, a tiny outpost of the park with a commanding view of the Pacific Ocean. The stuccoed developments of suburban Pacifica press in on the ridge and its rolling carpet of scrub and coastal prairie. At the height of the Cold War this was a missile base, with barbed wire and guard dogs. The ridge eventually made its way into the fold of Golden Gate. Jutting up above a sea of housing, it’s become a serene and defiant island, a refuge for threatened species such as the California red-legged frog.

Last year, in anticipation of its 100th anniversary, the National Park Service released its “Urban Agenda,” which is a continuation, although with more urgency, of earlier calls to action begun in the 1970s. What the report makes clear is that it is good business and—with America’s demographics changing rapidly—good politics to make the agency more relevant to an increasingly urban and diverse America.

One place where this new order is playing out is Indiana Dunes National Lakeshore, which nestles up to the steel mills along Lake Michigan in northwest Indiana and stretches into the largely hidden beachfront of Gary, one of America’s poorest cities. “Big parks deliver the wealthy, white, rich people,” said Paul Labovitz, the park’s superintendent. But the future of the Park Service means cultivating new visitors, and that’s easier for the urban parks. Because they are newer, Labovitz said, they have fewer traditions to get in the way of experimentation.

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View Images Silesia Park, Chorzów, Poland, opened in 1955 Wrested out of a wasteland of slag heaps, bootleg mines, and garbage dumps, this postindustrial landscape was transformed into a verdant area that includes a zoo and a dinosaur valley. Much of the work was done by volunteers coordinated by the Communist Party. In southern Poland’s urban core, the park is an inviting place for young people such as Maja Peryga, who visited the rose garden to photograph a friend.

The iconic urban parks with their straight borders and square shoulders aren’t going away. They are treasured in cities around the world. But the orderly layout they require is harder to find in places that are already built-up. So our newer urban parks, in the United States and beyond, reflect the challenges of acquiring and developing land. There’s now more review from the public as well as more oversight by regulators, said Adrian Benepe, the director of city park development for the Trust for Public Land and former New York City parks commissioner. Compounding the problem is the hunt for money to transform the bits and pieces of postindustrial landscape into parklands. “There is a struggle because the cities are also paying for health care and education,” Benepe said. “Often the parks are the last priority.” What’s emerging, he said, is a model more reliant on working with the private sector, both for building parks and for operating them. In Tulsa, Oklahoma, for example, a foundation created from oil and banking wealth has donated $200 million toward a $350 million community park on the Arkansas River. In Newark, New Jersey, Benepe’s group worked with government and business leaders to bring a park to once contaminated property along the Passaic River.

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View Images The Presidio, San Francisco, California, opened in 1996 Sunset and low tide lure walkers to Marshall’s Beach. Strategically located at the entrance to San Francisco Bay, the park was a military outpost for 218 years. Unlike other parks in the national system, it receives no federal money. Most revenue comes from renting out former military buildings. The sweeping views of the bay from the Golden Gate National Recreation Area draw visitors such as Ben Fernyhough, who came from Oregon on a skateboarding trip.

Perhaps the world’s most ambitious urban park run with this entrepreneurial mind-set is the Presidio, the former Army base that is part of Golden Gate Recreation Area but operates separately. Situated at the entrance to San Francisco Bay, the Presidio was first claimed by Spain, then Mexico, and finally, in 1846, by the United States. Peace did what wars could not, and in 1989 the Presidio was deemed unnecessary to the national defense, and the base—1,491 acres of barracks, buildings, valleys, and breathtaking vistas—was closed.

In 1994 it was transferred to the Park Service. Unlike other national parks, the Presidio has its own board of directors and now raises all its own revenue, mainly by leasing out the former military housing as well as the hospital and administrative buildings to residential and commercial tenants. The private businesses employ about 4,000 people, and more than 3,500 live on the rehabbed base. A house in one of the swankier neighborhoods, where the Army brass once lived, rents for $12,000 a month. The proceeds are plowed back into restoration, renovation, and maintenance. The cypress trees, planted more than a century ago, are dying and need to be replaced. Re-creating a wetland, part of a broad plan to restore biodiversity, would​ require tearing down less historic, but affordable, apartments, underscoring the constant soul-searching and rebalancing of competing missions.

“The overlay of values and land is more complex here than at any other place,” said Michael Boland, one of the Presidio’s top officials. The park’s assets, which brought in $100 million last year, are far from typical, but that obscures the larger point about urban parks, their fuzzy boundaries, and the compromises that they end up forging. “I think the future looks a lot more like this than it does like wilderness areas.”

View Images Cheonggyecheon, Seoul, South Korea, opened in 2005 Cheonggyecheon meanders through Seoul, South Korea. Once the city’s lifeblood, the stream was covered for years. Now it’s a place that embraces community and the soothing nature of water.

Wilderness can seem like both a bright line and an increasingly subjective description of an environment that has all but disappeared. With urban parks it isn’t about absolutes but often just about the joy of being outdoors. I was reminded of that when I visited Tempelhof, an airport turned park near the heart of Berlin. It was a weeknight, and in the hour before sunset people were pouring into the park. They rode bicycles on the mile-long runways and jogged around the meadows. Young men parasailed with skateboards, and mothers kicked soccer balls with their children. And because this is Germany, there was beer.

Tempelhof Airport closed in 2008. When it reopened as a park two years later, there was uncertainty about whether it would be embraced by Berliners. Then, as now, the park had few amenities; it was as if the airfield had just closed for a day so the tarmac could be repaved. But the authenticity—that it had been largely unaltered—proved key to the park’s appeal. Residents liked its openness and nearly unobstructed sunsets. They delighted in entering property that had once been off-limits. But most of all, they reveled in the sense of freedom found in Tempelhof’s 1.2 square miles. When city planners unveiled a proposal to build housing and office space on a fifth of the land, a backlash led to a referendum in 2014 that blocked most future development there.

“You can feel the sky. You can breathe,” said Diego Cárdenas, one of the leaders of the referendum movement, as we sat on the grass at Tempelhof. “If you start developing one part, where will it end?”

Tempelhof’s future still involves housing, although perhaps not in the way either side envisioned. Part of the terminal building, with its three-quarter-mile-long curved roof, is providing temporary shelter for some of the thousands of refugees who have poured into Germany.

With the clarity of hindsight, officials say the development plan was not well explained and they didn’t realize how people would respond once they were inside the park. Berliners have a history, they noted, of claiming unused open land as their own. At Tempelhof that happened on a colossal scale.

“They wanted to seize it,” said Ursula Renker, a planner with Berlin’s city government. “For most people, the airport was part of their history. There was a special fascination because it was so fenced in. You had to walk in through a gate.”

The gates are still there, and you can see people break into a smile as they pass through them. It is anticipatory pleasure, based on familiarity. Urban parks may not make our bucket lists, but they deserve a place on what I would call our coffee-cup lists.

And so it is with my favorite urban park, a wetland near my home. It’s nothing flashy, just a few acres of low ground that were spared development. I go there often. I like to get there in the early morning, walk among the cattails, and watch the two worlds—one of pavement and the other of the swamp—come to life. As the sun rises, catching the tops of the trees, the traffic grows along the four-lane roads that flank the park. Eventually, the noise becomes constant enough that it fades into the background. Then, if I listen carefully, I can hear the birds sing.