I’M A SUCKER for a post-industrial landscape. Unspoiled nature moves me as much as it does the next person, I guess, but give me a rusted-out mill or abandoned railroad tracks with my green and pleasant vista and I’m captivated. Suddenly the scene becomes a story.

So as soon as I learned about the Great Allegheny Passage (GAP), a bike path that winds through 150 miles of historic coal and steel country on derelict grades of the Western Maryland Railway and the Pittsburgh & Lake Erie Railroad, I started hatching a vacation plan. The GAP runs between Cumberland, Md., and Pittsburgh, Penn., and probes parts of Western Maryland and southwestern Pennsylvania no car can quite reach—places still firmly anchored in another era. Anyway, that’s how I pitched it to my friend Marne when I persuaded her to abandon her family in New York for a week and join me.

I rented a sturdy Trek Verve 3 hybrid bike and saddle bags at Golden Triangle Bike Rentals in Pittsburgh. For an added fee, owner Tom Demagall shuttled us from Pittsburgh to Cumberland, a drive of just over two hours. If all went according to plan, it would take us five days to make our way back.

And I do not mean five days of nonstop pedaling. We weren’t out to prove anything. Besides, we’d heard a biker-friendly tourist industry had begun to sprout up along the trail and we intended to avail ourselves of its comforts.

For starters, we skipped the steepest climb of the otherwise largely flat GAP—the stretch between Cumberland and Frostburg, Md.—by hauling our bikes onto the Western Maryland Scenic Railroad. We passed the time during the hour-and-a-half trip curled up in the lounge car’s leather club chairs sipping from a list of regional beers and wines while the antique steam engine did the climbing for us.

In fact, it was two days before we ever mounted our bikes. We spent them near Frostburg at Savage River Lodge, an eco-friendly resort in Western Maryland’s Savage River State Forest that caters to cyclists, fly fishers, bird-watchers, skiers and other outdoorsy types. For us, it was all about indulging in fortifying meals of grilled game and enjoying massages we hadn’t yet earned. At night we slept snug in a yurt, with radiant heat rising up through the floor and owls hooting in the branches outside. Roughing it minus the rough parts.

On the morning we reluctantly checked out, owner Mike Dreisbach shuttled us to the GAP trailhead, and from that point on, the sense of a place and an economy in transition remained with us the rest of the way, rendered all the more vivid by our mode of transport.

The rise of railroads in the 19th century spurred volumes of anxious prose: Everyone from Karl Marx to Henry David Thoreau fretted over the way this new technology obliterated space and time and cut people off from nature. Cycling accomplishes the opposite: At a bike’s pace, feeling every hiccup in the terrain and the weather, we were intimately attuned to the landscape around us.

And what a landscape it is. The first day brought some major-league milestones, including the Mason-Dixon Line and the Eastern Continental Divide. Big Savage Tunnel, at 3,300 feet the longest of several we would hit on the GAP, took us straight into the cool and murky depths of the mountain of the same name. I’d read that this stretch is honeycombed with old mines, but all we saw were wide green valleys and forested mountainsides. The only visible evidence of energy production were windmills—colossal, white, futuristic. (This is the edge of fracking country, too, but those operations remained discreetly out of view.)

We rode about 30 miles that day, stopping for lunch in Meyersdale, Penn., a tidy collection of clapboard houses and redbrick buildings running down a hillside. On the deck at Joe Greens Fresh Eatery, we ate delicious sandwiches of grilled chicken and fresh strawberries, chased by lemonade infused with the Appalachian fruit pawpaw. A few spandex-clad GAP riders were in evidence here, and a spin around the former coal town—the last major mine in these parts closed in the early 1980s—confirmed that a number of businesses, including a hotel, pubs and restaurants fitted with bike racks, had stepped up to serve them. Once a railroad hub, this town is determined to draw another kind of traffic.

Just past Meyersdale, we felt like we were flying as we rode across the 1,900-foot-long Salisbury Viaduct, a steel trestle that carried us high over the Casselman River valley. Once across, we rode through miles of forest, with blooming mountain laurel lining the path on either side. That night we stayed at Horizon View Farms, outside the town of Rockwood, where a pot of chili awaited us in the kitchen, along with a pie and a bottle of wine.

The only guests that night, we had the run of the property—the kind of thing that can still happen off the beaten path, and a luxury in itself. We ended the night under the stars, beside a fire we built in the pit by the weathered wooden barn.

In the morning, we set out on the roughly 30-mile ride to the town of Ohiopyle, an affable hippie outpost overlooking a roaring waterfall at the heart of Ohiopyle State Park. Here, in 20,000 acres of old forest, the Youghiogheny River cuts through the Laurel Mountains to form the deepest gorge in Pennsylvania.

It’s a landscape that could turn an architect’s head, and has: The area claims a couple of significant Frank Lloyd Wright properties. I’ve visited the more famous of the two, Fallingwater, many times and so decided to check out Kentuck Knob. The low-slung sandstone structure, nestled into the crest of a mountain ridge, presents not only a staggering panorama of the Laurel Highlands but also a blue-chip collection of contemporary sculpture— Andy Goldsworthy, Claes Oldenburg, Anthony Caro and the like—installed around the grounds.

Our final day of pedaling would hurtle us out of the forest primeval and smack up against the industrial age, the steel mills rising up along the river on the approach to Pittsburgh. In the woods just past the old company town of Buena Vista, we came upon a blood-red waterfall cascading right alongside the path. A plaque explained it was the result of acid drainage from a mine abandoned in 1938 but certainly not forgotten. It stopped us short—gruesome, unnatural and at the same time weirdly beautiful. The story a rust-belt landscape has to tell isn’t always a happy one. But you can count on plenty of drama.