(FORTUNE Small Business) – When the weather turns Chilly, most mountain bikers push their bikes into the garage and keep them there until spring. For one biking devotee that wasn't good enough. Ray Petro, 39, a remodeling contractor in Cleveland who took up mountain biking nine years ago, wanted a place he could ride year-round, even during the worst Midwestern winters. So he built one himself.

Petro invested his $50,000 life savings and took out a $25,000 loan to launch Ray's Mountain Bike Indoor Park, which opened in November 2004 in a warehouse just west of downtown. In the year since, his venture has been so successful that Petro has scaled back his contracting business to summers only; the other nine months he runs the park full-time. "I've gotten e-mails and calls from people," he says. "Some say, 'You stole my idea.' Others say, 'You're living my dream.' "

Every month about 1,000 mountain bikers ride at Ray's, and most of them heard about the park from other customers. "I paid for some posters and stuff, but that's about it," Petro says of his modest marketing efforts. Several times last winter busloads of bikers arrived from Toronto. A local Holiday Inn offers a Weekend at Ray's special--$59 for two nights, including entry to the park. The regular one-day rate is $15, and so far Petro says he's on track to break even in two years.

One early skeptic of the idea was Joe Prisel, 33, a pro mountain biker from Parma, Ohio, who competes internationally (most recently in Peru) and builds courses for competitions across the U.S."I heard the buzz, and I wanted to check it out," Prisel says. "Actually, what I had heard is that this place would never work." But Prisel quickly became a believer--and the main architect of the course. The wooden ramps and obstacles look primitive, but Prisel used CAD software to design many of them, often tweaking the plans during the building process. Much of the construction was done by the Founders Club, a 12-man crew of Petro's mountain-biking buddies who helped him build and test the obstacles. In return for their labor, the Founders ride free.

The warehouse had been around for almost a century before Petro bought it in July 2004. It formerly housed a manufacturer of brakes and water pumps and, in the 1920s, silk mills that made parachutes for U.S. servicemen. Now bike racks line the loading-dock entrance, and a graffiti wall that customers sign in place of a guestbook is tattooed with the names, cities, and states they come from--Chicago, Maine, and Pittsburgh, among others.

The 71,000-square-foot park is divided into three tracks and three stunt areas for bikers of varying abilities. A beginner's course consists of gentle, two-foot ramps and obstacles. Petro insists that you don't need any experience to ride the beginner course. I'm living proof that this is true--I hadn't been on a bike since junior high, but I survived a lap through it on one of Petro's rental bikes. At the other end of the warehouse the expert course looks like a construction zone, with a box jump, "technical skinnies" (two-by-fours that double as balance beams), and six-foot drops suitable only for veterans. There's even a four-foot-deep foam pit where bikers can try jumps and land without much risk of getting hurt. Similar to an above-ground pool, the pit is filled with foam strips. You can ride your bike into it or leap off a six-foot-high platform.

Ray says the facility appeals to a seasoned crowd, many of them ex-BMX bikers who grew up, got jobs, and now are too old to frequent skateboard parks. Most are in their 30s, though the clientele ranges from 16 to 60. "Ray's has brought many people out of the woodwork," says Lawrence Kuh, a teacher who sometimes totes along his 7-year-old daughter, Masie, on Saturdays when he comes to the park. "It's giving us sanity because we can ride year-round."

Petro has already garnered some attention from bigger companies. Gary Fisher Bicycles (a division of Trek) recently gave him $5,000 to help build one of the newest stunt areas in the park. "It was a perfect match for us," says Ryan Atkinson, assistant brand manager for Gary Fisher Bicycles in Waterloo, Wis. "His category--free riding--is one of the fastest growing in our industry." Atkinson also struck a deal to make Gary Fisher the official supplier to Ray's, providing bikes for test riding and for Petro to travel with when he promotes the park. Similarly, Subaru donated money to help build a stunt park in a corner of the warehouse, which was designed by Joe Prisel and is currently under construction. It's similar to a skateboard park, but has larger curves to accommodate bike frames. The Subaru name will be featured prominently. And last year Red Bull sponsored a jump contest at Ray's, bringing in one of its athletes to compete and sign autographs. "From a corporate perspective the park mirrors what Red Bull is about," says Alfie Brody, field marketing manager for Red Bull North America. "I love the concept so much I'm trying to help him enhance the interior."

Despite such corporate interest, Petro remains most focused on improving the course. It's like making a new recipe," he says. "It's never as good until you do it a few times. I did my best shot to get the park open, and now I've seen what people love, what people don't like, what is safe, and what could be safer."

Petro will continue expanding, and his crew will fill in the few empty spaces left in the warehouse. Besides building up corners, he plans to rearrange obstacles, move ramps around, and reorient the course to make it longer, larger, and better for its second season. "I'm looking forward to improving on my first attempt," he says.