On the tracks of a railway depot in northern France, a steam locomotive puffs out smoke as if it just took a drag. An engineer and two apprentices stand inside its teal-colored cab wearing dark clothing and gloves. It’s hard to make out their faces under the glare of the midmorning sun. They’ve been warming up the engine for three hours and are ready to roll out.

One of the apprentices leans against the open window with his arms crossed, contemplating his work. What excites him most is “to feel the machine live,” he says, gesturing around the cab as it shakes, jolts and howls, as if to say, “See?”

This is the Chemin de Fer de la Baie de Somme. This 19th-century railway connects the towns of Cayeux-sur-Mer, St.-Valery-sur-Somme, Noyelles-sur-Mer and Le Crotoy on the Picardy Coast of France, where the narrow Canal de la Somme expands into the vast estuary that joins the English Channel.

There is everything and nothing to see in these towns. Bike paths carve through fields of yellow flowers. France’s largest seal colony bobs around in the water, disappearing and reemerging to the delight of boat tour operators. At dusk, starlings ebb and flow through the sky. Landscapes really bring the drama.

In Cayeux-sur-Mer, a beachy town along the channel, an endless array of cabanas stretches across the boardwalk, and bronzed old ladies sit outside on plastic chairs, greeting anyone who walks through their territory. (If it’s an overcast day, they migrate into the seaside casino’s restaurant.) Three-hundred-foot chalk cliffs render beachgoers minuscule in the scenery’s display.

There are no big “sites.” The boundless estuary, medieval walls and coastlines just exist in the landscape.

I stumbled upon the chemin de fer (railroad) last year. My neighbor and I had been commiserating over our hangovers in Paris and started daydreaming about the sea. “If we find a ticket for under 20 euros, we’re going,” we said. A search led us to Noyelles-sur-Mer, a town too small to have a bakery or a tobacco shop, effectively a mark of urban legitimacy in France.

When we arrived in Noyelles-sur-Mer, the whistle of the steam train got our attention. Since our first ride, it’s been hard to stay away for too long.

Running on volunteers

Between carriages, wind whips through an open-air ­corridor connection and metal clashes on the track. The clicks and clacks, roars and ­double-thuds come together like a song as the train curves, lightly brushing against tree leaves. The horn whistles. The wood creaks. A butterfly flutters between cars like a tease, lingering just long enough to flash the cobalt on its wings before narrowly escaping the car. The rickety vibrations leave me feeling slightly dizzy, mellowed out and high in a way that some people might pay for.

Alain Paillard is the vice president of the nonprofit Chemin de Fer de la Baie de Somme, the association that runs the railway with a few paid employees. We meet at the depot in St.-Valery. When he smiles it’s impossible not to smile back.

He tells me that he had an uncle, a steam train engineer, whom he would visit on vacations. “When you’re this tall” — he holds his hand about 3 feet off the ground — “and you stand in front of an enormous machine like that, it’s impressive, it marks you.”

During World War I, the British army used this railway to transport troops and equipment, especially throughout the Battle of the Somme. But the railway’s infrastructure was seriously damaged — many of the locomotives, cars and tracks were destroyed. The network was rebuilt from 1919 through the early 1920s, which is why so many of the railway’s cars date back to then. (The year a car was made is marked by a plaque on its side.)

Since 1973, the railway has been fully in the hands of the nonprofit association. Volunteers are critical to the restoration effort — every Thursday, electricians, painters and train aficionados meet to rebuild, paint, polish and maintain the network.

In the workshop, monstrous engines line the center of the room like an industrial fashion catwalk. Every few minutes, someone pops a head out from the machinery, joking with Paillard about sooty clothes or beer bellies. It’s loud. Katy Perry’s “Hot N Cold” plays on the radio against the backdrop of power tools, screeching and clanking.

Every piece of every train has a story. Paillard knows them all. We approach steam locomotive No. 2.

“Here, it says FCPR, which is Spanish,” he said, pointing to the plaque on its side, eyebrows raising, eyes widening, shaking his head as if he can’t believe what he’s about to recount (the initials stand for Ferrocarril de Circunvalacion de Puerto Rico). “I’m going to tell you this extraordinary story.”

The French-built engine was commissioned in 1889 to help transport materials for the French effort to build the Panama Canal, led by Ferdinand de Lesseps, who had directed the Suez Canal project 30 years before. The effort eventually failed, and the steam engine was sold to the Puerto Rican railroad, where it hauled its first passenger train in 1891.

That railroad eventually modernized its infrastructure, so the locomotive was taken to the Henry Ford Museum of American Innovation, where it stayed from 1929 to 1977. When the museum reviewed its collection and decided to let the engine go, it was purchased by a bank in Traverse City, Mich., that was situated in a former train station. It ended up back in France in the 1990s, and is now in ­service on the St.-Valery-Le Crotoy line.

The trains — which run every hour or two depending on the day and route, and cover about 17 miles of tracks — are critical to getting around the area without a car (from 13 euros, about $13.75, for a single-ride adult ticket). Buses are scarce and slow, while taxis are hard to find and expensive.

A crossing at low tide

There is another way to cross between Le Crotoy and St.-Valery, the towns that mirror each other across the 2-mile Baie de Somme estuary — by foot, at low tide.

From Le Crotoy, where Jules Verne drew inspiration for the novel “Twenty Thousand Leagues Under the Sea,” St.-Valery looks almost like a mirage. At 5 p.m. on the banks, a guide leading the crossing squints to carefully scan the stretched-out expanse of nothingness that lies ahead, neck slightly craned forward, walking stick in hand.

“I strongly recommend that you take everything out of your pockets,” he yells, herding the group down to the mud flats to wade through a short stretch of knee-deep water. “You can cross barefoot if you want.”

We move quickly. If the group is too slow crossing the muddy crevasses between the marshes, some involving near-vertical slick climbs, the tide will rise, there would be an hours-long detour and worse — everyone could kiss apero (aperitif) hour goodbye, our guide threatens.

Over the brisk three-hour walk, dozens of arms wave for balance in the air, seemingly touching the sky.

Eating along the bay

The next afternoon, back in St.-Valery — where William the Conqueror assembled his fleet in 1066, Joan of Arc was held prisoner and Edgar Degas painted — I set off for a walk.

In the center of town against the backdrop of the estuary, food shops sell gift-wrapped bottles of vinegars and specialty mayonnaise. The mini-golf course looks like the site of a utopian experiment. Mealtimes are rigid, and almost all restaurants shut down by 10 p.m.

Push outward a little bit and things get cooler.

Cobblestone streets give way to vibrant houses draped in flowers, winding uphill through medieval walls against endless, saturated panoramic views of the bay. Down one of the steep leafy pathways that jut off the Rue Jean de Bailleul, La Buvette de la Plage serves fresh whelks, shrimp and oysters, in addition to regional classics like the ficelle picarde, a thick crepe stuffed with cheese and various savory fillings, right on the bay (from 9 euros). Lounge chairs on the silty shore overlook the water.

Across the locks on the canal, on the southern end of St.-Valery, La Canoterie offers shellfish, casual plates and drinks, with picnic tables and some chairs overlooking the water (from 7.50 euros). It wouldn’t look out of place in upstate New York. But it’s more than just a restaurant — they rent bikes and run canoe, kayak and walking tours (10 to 30 euros).

On the way back to Paris — in what is usually an under-two-hour journey on the TER regional train — my train got stuck for an “indefinite amount of time” in a small town, prompting a symphony of collective groans and bad words.

Hours after we had been scheduled to arrive in Paris, the doors beeped to signal closing, the engine started vibrating, and we slowly moved forward. Passengers clapped and cheered, smiling at one another and cracking jokes. Feeling the machine live is, indeed, awesome.

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