Imagine cycling the perimeter of O'ahu 50 times; that's about 6,200 miles. Then, make 650 of those miles across the Uzbekistan desert where roads disappear beneath deep sand, and temperatures force travelers beneath a tarp to escape the blistering heat of the day.

Scorpions, tarantulas and black widow spiders live in the sand beneath your tent but above, the night sky is spectacular.

The horizon is empty except for barchan dunes — arc-shaped ridges of shifting sand and gravel. But this is the Old Silk Road. It has carried people, goods and ideas between Europe and Asia for centuries.

Camels still travel this route, as do adventurers. Among the latter: Blaise Trigg-Smith, 28, and Tom Damek, 30, who left Germany in April to cycle to Kashgar, China, one of the oldest trading cities in the world. Their journey spanned more than 6,000 miles.

"A friend had told me he was going to cycle around the world," Damek said. "I ran into him again and he'd actually done it. It was inspiring; I thought, if he can do it. ..."

"And we both had desk jobs," said Trigg-Smith, who grew up in Kailua and is based in London. "We're both athletic; we love sports. This just felt like a great adventure."

The couple also wanted to raise money for two charities.

On paper, the plan was simple: Cycle from Germany to China, roughly keeping to the ancient Silk Route; follow the Danube through Europe; then cut across to Istanbul, Turkey and into Asia. After crossing the Caspian Sea, the route continued through Central Asia — the former Soviet "Stans" — across the steppes and high mountain passes and finally into Western China.

"The Silk Road is one of the most ancient trade routes going through hugely diverse countries and cultures," Trigg-Smith said. "We wanted to really see the countries. Going by bike is just about slow enough to take in everything and fast enough to cover some real distance."

Carrying everything in panniers on mountain bikes, Trigg-Smith and Damek set off on a remarkable journey, each day an adventure through cities, villages and across largely unknown landscapes.

They repaired tires, camped in fields, faced down weather and met with locals. They waited hours for unpredictable ferries to leave foreign ports.

Waiting at Baku, Azerbaijan, for a ferry to cross the Caspian Sea to Turkmenistan, they heard the country was closed to travelers because of swine flu restrictions.

So, to Plan B: Trigg-Smith and Damek changed their route to cycle instead through the Uzbekistan desert, a terrain so challenging that even veteran travelers cross it by train or plane. It is as far off the beaten track as Asia gets.

"We knew we were in for one of the toughest stretches of the journey, Trigg-Smith said, "... 650 miles of desert with almost nothing along the way."

INTO THE OVEN

Uzbekistan is a double-landlocked country, surrounded by countries also landlocked. Its cities are legendary: Khiva, Bukhara, Samarqand.

As a way station on the Old Silk Road, Uzbekistan's history developed through centuries of welcoming strangers. But outside of the cities is desert. Two deserts, actually — the Kyzyl Kum (red sand) that merges with its northern neighbor into Kazakhstan, the Kara Kum (black sand).

Crossing the Kyzyl Kum would mean extra loads on already heavy bikes: 10 gallons of water, food for at least a week, increased mental and physical stamina.

Sand and gravel roads promised difficult cycling. And would a ground sheet and mosquito net ward off the killer spiders everyone talked about?

Undeterred, they set off.

"One of the best parts about the steppe was that we could camp anywhere," Trigg-Smith said. "There was no shelter, of course, but with nobody around and completely flat land stretching to the horizon, the choice was ours."

Desert travel meant rising with the sun, resting for hours during the heat of the day and then cycling late in the evening. A tarp secured over the bicycles provided shelter from daytime temperatures that soared well above 110 degrees. They saw scorpions but no black widows.

Meals were nutritious but repetitive: pasta, rice and cracked wheat mixed with powdered milk, canned vegetables and fish. As drinking water heated up during the day, they added tea leaves for "automatic tea."

And there was boredom.

"There is a great nothingness in the steppe," Trigg-Smith said. "The uncertainty of when we would reach something was definitely one of the most difficult parts of the journey."

But the desert has its rewards: The sight of hundreds of camels crossing the steppe; night skies filled with brilliant stars, a profound silence.

Several days later, covered in sweat and dust, they pedaled into Qonghirat where the landscape was lush, green agricultural land of the Amu-Darya basin. Dried food gave way to watermelons, peaches and grapes.

While the Uzbek desert proved the toughest challenge yet on their journey, reaching Khiva, one of the best preserved of the Old Silk Road cities, was a highlight of their trip.

"We had made it that far, and we were really pleased. (Crossing the desert) was definitely not great but it felt great to have done it," Damek said.

Were they saddle-sore? Yes. Had it tested their relationship? "Actually, we found there wasn't really that much to fight about," Trigg-Smith said.

"It was really an epic journey, a fantastic, challenging, rewarding and unforgettable time. I'd say it brought us closer to knowing each other."

MAKING IT

On Sept. 11, 2009, Blaise Trigg-Smith and Tom Damek reached Kashgar, China, after five months on the road and almost 6,300 miles on the pedals.

They raised more than $20,000 for charity. Read their blog at http://happypedalers.wordpress.com.