By STEPHEN REGENOLD

The battle began at 7:30a.m., a shout initiating a bike race from a park on the banks of the Mississippi in southern Minnesota. Tires rolled, gears clicked, and 65 cyclists pedaled from light into shadow on course toward a day of pain.

It was mid-April, a Saturday in Goodhue County, where river bluffs prop like walls above farm fields and trickling streams. The Ragnarök 105, an underground race organized by three bikers from Red Wing, Minn., snaked south toward its first test of vertical relief.

In the next 105 miles, the course, which winds on gravel roads in Goodhue and Wabasha counties, would roll and ascend for an estimated 8,000 feet of elevation gain.

“We mapped out the biggest hills from our training rides,” said Isaac Giesen, an organizer, “and then we connected the dots to create this course.”

The result is a precipitous and serpentine tour of the steepest bluff country Minnesota can offer. Ascents begin from valley depths, rising on roads that climb hundreds of feet in less than a mile. Thighs burn, wheels spin, tire tread searching for grip on gravel and sand.

Ragnarök organizers provide no maps. The course is not marked. Racers follow card diagrams with directions and arrows, squinting to see road signs, tracking distances to the tenth of a mile to avoid a missed turn.

“It’s not hard to get lost out there,” Giesen said as I signed a waiver after sunrise the morning of the race.

My journey to the start line began with a postcard mailed to Giesen’s home address in Red Wing. The Ragnarök, now in its second year, is open at no charge to the first 60 or so cyclists who mail a confirmation card.

The field is primarily Twin Cities riders, with mountain bikers, roadies, and urban commuters who pedal single-speed bikes. This year’s event, on April 18, drew 60 men and five women to crank for hours on end with no support and scant stops for water or food.

I pedaled a cyclocross bike, which is a hybrid model made for road and trail, and wore a backpack with water and supplies. The Ragnarök — a race named after a Norse epoch of apocalypse and doom — draws a serious group of cyclists. On the race’s long and climbing course, my hope was to finish in the middle of the pack.

But the Norse gods, I would find, were not with me that day.

An hour into the race, sweating on a gravel ascent, I looked into a ditch to see the bleached ribcage of a deer or cow long dead. “A racer from last year,” joked Shawn Jeppesen, a friend I pedaled with for half the course.

We were in last place, spinning hard to catch up. A string of breakdowns — a flat, a broken valve, and a punctured tire patched ad hoc with duct tape — had put us almost an hour behind the front.

Then we took a wrong turn, coasting three miles out of the way. “Bad luck,” Jeppesen said at the turnaround.

But by Zumbro Falls, the halfway point, we’d passed a handful of racers. I refilled on water, drank an energy shake, and clipped in feeling recharged for the ride.

It was 12:30p.m., and I was 55 miles down the line. The winner, Charlie Tri of Rochester, would soon cross the finish in Red Wing, smoking the course in 6 hours and six minutes.

My race — a lone endeavor after the halfway mark — settled into a groove. I paced 30 fast miles to Lake City, rolling along the Zumbro River and past small farms with chickens running free.

But the hills never seemed to stop. Gravel lanes meandered up and up. Near mile 90, on a road called Circle S Trail, I took a huge breath and pedaled at what looked to be a wall of sand.

The road topped out near a farm, a horse eyeing me behind a fence. I clicked into a higher gear and cranked, almost done.

Battling at a slow pace, I kept on. Circle S Trail to Cty. 21, then a right on Lehrbach Rd. Words blurred on the direction card.

I gripped the brakes, a final swoop from the hills toward town. Nine hours and 100 miles under my wheels — Norse gods with me or not — I wasn’t about to give up the fight.

(For race results and registration info on next year’s event, go to: http://ragnarok105.blogspot.com)

—Stephen Regenold writes a daily blog on outdoors gear at www.gearjunkie.com.