The whirring bikes streaked over the rough ribbon of asphalt through the Sahara in Mauritania, and the intensity of the landscape shifted.

Miles of flat, desolate sand stretched to the horizon in all directions, dissolving into an immense dome of pale blue.

The sun in the cloudless sky was so searing it had bleached the bones of a camel protruding from the sand.

A headwind, relentless and gusting, drained legs and thrashed the robe of a tribesman striding along on the roadside.

Then there were the tractor-trailers. Every 10 minutes or so, an oncoming rig appeared in the distance, gathering sheets of swirling sand in its wake. With only two tight lanes, the best recourse was to grip your handlebars and duck as the truck roared by, its vortex jerking the front of your bike and sandblasting every piece of uncovered skin.

In the fast-growing category of adventure cycling vacations, it’s safe to say that this one — West Africa en Velo, TDA Global Cycling’s first expedition through West Africa — was on the extreme end. Not just for the duration — nearly 4,000 miles through seven countries and one disputed territory over 10 weeks, averaging about 70 miles a day — but for the location. The region has been more associated with civil war, disease and extremists than bucket-list challenges. But as political and economic stability has increased in recent years, so has the number of foreign tourists.

The idea was to cycle and camp from Casablanca to Cape Coast in Ghana, through the Atlas Mountains in Morocco, the desert in Western Sahara and Mauritania, and rolling farmland, tropical forests or palm-fringed shores in Senegal, Guinea, Sierra Leone, Ivory Coast and Ghana.

Dozens of cyclists signed on for the trip, which cost $12,900 for the entire 72-day, 3,865-mile ride; those, like me, who joined for a two-week section, paid $2,900.

Riders — most in their 50s and older, many from North America and Europe, and a third of them women — brought their own bikes and camping gear, which was carried ahead each day in a truck. A van would stop and set up lunch around the halfway point of each ride, while tour leaders covered the route in SUVs, with a staff member riding sweep behind the group. Those who couldn’t complete the day’s section could hitch a ride on one of the vehicles.

Most people on the ride were strong cyclists and veterans of one or more TDA tours, keen to conquer a new frontier. They do the rides because they have the money, the time and the inclination, and for deeper reasons tied to wanderlust, ego, camaraderie and mortality.

“Multiple times when we go out on a ride in the course of a day, you get something that’s extremely tiring or exhausting,” said David Jones, 61, a former candy company executive from Toronto. “And just as you’re thinking, ‘Geez, man, I don’t want to do this,’ the road turns and you get a tail wind, or you get brand-new pavement or smiling kids at a village. I think it’s a great place to learn the benefit of hanging in there, just keeping at it.”

Mile 15, Western Sahara

I joined the tour in late October, 1,100 miles into the ride in Western Sahara, the disputed territory south of Morocco that is claimed by that country and the Polisario Front separatist movement. This two-week section would stretch 800 miles down the coast through Mauritania and into Dakar, the boisterous capital of Senegal. On my first morning, I pedaled hard for a half an hour to catch two riders ahead of me as the sun rose over the desert.

The pair — Annegrete Warrer, 65, who lives in Austria, and Hanne Renland, 62, of Norway — had met on their flight from Paris to Casablanca three weeks earlier and became close friends. Warrer was on her seventh TDA tour and riding until Dakar, and Renland, who took up cycling in 2017, was on her second and riding the whole route.

“We want to live life to the fullest,” Renland said, as her bike computer displayed 35 km/h, or 22 mph. “It’s time to put some K’s down.”

We rode flat out for a half-hour. The cobalt ocean was on our right as we passed several kite surfing lodges on the Dakhla peninsula that cater to a growing number of European visitors. We were flying through the salt air as sea gulls veered overhead. Spotted butterflies flitted around our bikes.

We rested near an abandoned desert village, a few square blocks of empty, one-story concrete buildings and a silent mosque. I asked them what they liked about the tour.

“It’s the total experience,” said Warrer, who used to own a travel agency. “It’s an everyday thing that we have; the rhythm, putting up the tent, sleeping, eating together, going out on the bicycle and then seeing if there is something interesting to engage us along the way.”

Renland, a psychologist who runs an educational charity in Tanzania, said she was inspired to cycle when she attended a presentation by a fellow Norwegian who had biked the continent of Africa from north to south.

“It’s like when you discover something you didn’t know you could do; then it’s so funny to explore how far you can go,” she said.

Two hours later, we rolled up to our desert camp, completing one of the tour’s longest rides, 100 miles. My crotch was raw, my legs were spent, and my feet ached from my cycling shoes.

There was no rest yet. I was introduced to the routine that the three dozen other riders had already adopted: Lug your duffel bag down from the truck. Find a spot and pitch your tent. Fill a bucket for a splash bath. Gather for the riders’ meeting at 5:30 p.m. Line up for dinner of rice and chicken or pasta and meat. Sit around and talk about the ride, past rides and injuries. Grab a shovel and dig a hole for a toilet. Duck into your tent. Collapse exhausted, usually by 8 or 9 p.m., to wake up at 5:30 in the chilly morning dark.

That night, the wind was gusting and my one-person tent was buckling as we slept under a vault of glittering stars.

Mile 232, on the border with Mauritania

The crossing into Mauritania took us through a forsaken stretch of land a couple of miles long, like a scene out of “Mad Max.”

After getting our passports stamped at a border checkpoint controlled by Morocco, we rode into the buffer between the countries on a rutted road. Amid the trash and sand off to the right were long rows of battered, abandoned cars. Men in robes with scarves covering their faces were moving through the makeshift junk yard, calling out to us in French.

Parked in the left lane, a line of tractor-trailers extended for a half mile, some with rocks wedged under tires. Drivers said they waited days for inspections and entrance into Morocco.

The road turned to deep sand and jagged rock, wending through barren flats up to two small buildings where touts called out, “Whachu need, whachu need.” They carried wads of cash, stacks of phone cards and cartons of cigarettes.

We waited in a sunny courtyard with four young Belgians and locals in colorful wraps and billowing robes. The line moved slowly to the two visa officers who sat in a dingy office with cardboard taped to the window to block out the sun. By the time they took our fingerprints and photos and we handed over 55 euros each, nearly three hours had passed.

“This is harder than the riding,” Warrer said as we headed to our bikes.

Mile 427, heading for Nouakchott

I spent the most time on the ride — seven days — in Mauritania, which like several other countries in the region gained independence from France around 1960. The impoverished Islamic republic is covered mostly by desert. It has a ban on alcohol and an abundance of beat-up Mercedes discarded from Europe. It was the last country to outlaw slavery, in 1981, and is thought to have links to terrorist groups.

The U.S. State Department advises citizens to “reconsider travel to Mauritania due to crime and terrorism.”

The biggest threat to riders is not getting attacked by militants but being hit by a driver, Henry Gold, the owner of TDA, told me as we chatted at a campsite one night.

He used to run a nongovernmental organization in east and southern Africa before starting TDA in 2003 with its flagship expedition, Tour d’Afrique, a four-month ride from Cairo to Cape Town. Now TDA runs 16 tours on six continents, one of a handful of operators offering multiple-country odysseys.

“The reason I did Tour d’Afrique, even though other people said I’m suicidal, is that I knew Africa,” he said.

There were a few areas that he was unfamiliar with, and to make sure they were safe, he took the same steps that his staff members followed before this West Africa tour. Theydrove the prospective route several times and talked with government and security officials, diplomats and NGO workers. A big advantage, Gold said, is that police and military commanders are determined not to let anything happen to a group of international tourists on their watch. Gold said TDA provides the authorities with the cycling route, and they determine the level of security.

On our last night in Mauritania, soldiers in three trucks came roaring into our camp with spinning lights and machine guns mounted on the roofs. They took up positions on the periphery of our tents. When we walked over to talk to the commander, he said they were there to make sure we were safe.

Between the Moroccan border and the Mauritanian capital of Nouakchott, there were occasional checkpoints where police waved us through, and random herds of goats or camels crossing the road. Villagers warily stared at us or exchanged greetings in French, and children ran into the road, hands out for whatever we might offer. At one stop I was surrounded by boys calling “ca va” and slapping me on the backside as I rode away.

“We are having fun now,” Christine Rousseu, a 65-year-old nurse from Montreal, one of a dozen Canadians on the trip, shouted as a rig blew past us on our 90-mile ride into the headwind.

Rousseu often was in the back of the pack, riding solo, as she prefers. She has done cycling tours on her own or with TDA since 1980 but has been ill in recent years, she said. “I’m not supposed to be here,” she told me. “I prayed a lot to return to my health to be able to suffer again on my bicycle.”

She said this would likely be her final TDA ride. Some of the cyclists were too competitive, and, she said, it seemed to her that as soon as she pulled up to a Coke stop or lunch, “they jump on their bikes and go, go, go,” because they didn’t want to arrive at the next stop after her.

A couple of days later, on our rest day in Nouakchott, I told her that I had been talking with some of the younger riders — in this case a group of men in their 40s and 50s — who singled her out as an inspiration: “Ordinary people doing extraordinary things every day,” as one of them put it.

She looked at me for a moment and her eyes welled up. She touched my arm and walked away.

Mile 644, into Senegal

Over the days, I’d heard some riders talking about whether these expeditions were the hardest things they’d done in their lives, how many of their friends and relatives thought they were crazy. I asked riders whether they were missing a gene for sensitivity to pain and suffering.

“I think all agony and frustrations fade way over time and I just remember the happy points,” said Caroline Derouet, a 43-year-old forensics officer in a police department near Toronto. “It takes awhile for the degradations to just kind of be part of your daily life. I think we all go home with a sense of gratitude at how easy we have it.”

The most common ailments were related to sore bottoms and diarrhea. After a few days, I lost strength in my hands, but they improved when I added padding to my handlebars. Over the tour, several riders were sidelined with infections or viruses for days or weeks, and two were seriously injured in crashes, including a broken arm and a broken collarbone. Of the 33 people signed up for the whole ride, 28 finished.

On our first full day in Senegal, the desert was behind us and the 70-mile ride ahead would end at the former capital, the small island of Saint-Louis.

We spun past lush rice paddies and fields of corn and sugar cane in the Senegal River valley. The traffic was heavier, including bus-like Mercedes vans often so stuffed with passengers that several men stood on back platforms.

After 45 miles my head ached and my legs were sapped. I reached the lunch truck under the shade of a thorny acacia tree and got a second wind. I paired up with Trixie Wagner for the rest of the ride.

Wagner said she took up triathlons as she neared 50 a few years ago and was using this tour in part to train for her third Ironman. A scientist at a drug company in Switzerland, she has developed a radical work-life balance. She works full-bore most of the year, at times putting in 14-hour days, then plunges into her passions of cycling and photography for extended periods, as on this 10-week ride.

“It really reduces your day to the bare necessities,” she said. “It’s a total reset.”

We tooled past the once-grand French Colonial buildings of Saint-Louis and over another bridge to a busy waterfront crossroads where Wagner took photos.

We finished the day with a leisurely ride to a beach camp with bungalows and a bar. At the riders’ meeting, our Senegalese tour guide, Philippe Nelson Ndiaye, 29, told us how the stable democracy was abuzz about the coming presidential election and how a cemetery in the middle of the country that holds Christians and Muslims speaks to Senegal’s tolerance.

Mile 725, onto the beach

The next day our ride along a deserted, hazy stretch of beach turned into a 25-mile slog.

“This is where people start to explode,” said Gold, as we surveyed the roiling Atlantic.

The rutted and sandy, 12-mile road to the beach had already drained us. Now the temperature was over 100 degrees andlow tide — and hard-packed sand for smooth riding — was still a couple hours away.

Searching for a strip of firm sand, right at the edge of where the waves crest was exasperating. Sudden waves raced up the shore and swamped our wheels, knocking over some riders and leaving many of us pushing our bikes.

After an hour, there was more ebb than flow and the wind was at our backs. We waved from our saddles at the occasional horse-drawn cart, frowned at the multitude of discarded plastic bottles.

Several riders had a meltdown in the sand, and Jones was on the verge. But his partner, Mimi Viviers, a South African he had met three years ago on the Tour d’Afrique, rode back to give him a hug and a pep talk.

“I often tell my kids that cycling is very much like life,” Viviers, 56, a retired telecom consultant, said later. “If you see a hill, it always looks worse than it is. You just take it in small chunks.”

At the campsite that night, as we feasted on roasted goat and couscous under a tent, tour leader Max Dionne had an announcement. Nodding to widespread grousing and the reality that low tide was coming too late in the day, he said, “Tomorrow we do a change. We’re not doing a beach ride.”

From the tables came a sarcastic, collective, “Aaaawwwww.”

Mile 820, the final stretch to Dakar

On my final day, the 30-mile ride was supposed to follow the coastal road to Dakar, the first four-lane highway of the trip. But there was an option for a beach ride, and five of us signed waivers exempting TDA for any mishaps on our detour.

We rolled out of camp and passed Lac Rose, a saltwater lake with algae that at times makes the water pink. But on this hazy morning, it was glossy gray. Shirtless men in waist-high water scooped out the salt crystals for sale to gourmets in Europe.

When we reached the ocean, the breakers swamped us again. As I swerved up the slope trying to dodge a wave, my gears hopped and my chain busted — my only malfunction of the tour. This was a problem, because I had no idea how to fix it and the waiver made it clear we were on our own until the hotel. Luckily, Andre Marcoux, our informal leader, had the right tool.

Twice we had to move the bike to higher ground as the tide swept in. When I told the group to go on without me. Marcoux, a 65-year-old retired forest engineer, insisted, “It will work.” After 25 minutes the chain links were coupled, and we rode to the route’s end and had a swim in the surf.

For the next two days, we rested in the sprawling capital. We tried the local fish and rice dish at seaside restaurants. We piled onto a ferry for a tour of the Goree Island, where former slave-trading houses and narrow stone lanes shaded by bulky baobab trees were crowded with Western tour groups.

Although I was glad to see the end of bush camping and pedaling eight to 10 hours a day, I also wanted to continue. But my ride was finished. The group had 2,000 miles to go.