YOU COULD BE FORGIVEN for doing a double take near Exit 168A on Seattle’s I-5 these days. At first glance, the wood and stone structures that have sprung up just north of the off-ramp might be enough to make you think a colony of wayward Ewoks has set up camp under the highway between Eastlake and Capitol Hill. But the actual inhabitants of the I-5 Colonnade look more like Stormtroopers. Watch for a while longer, and you’ll likely see a mountain biker clad in body armor and full-face helmet, balancing a few feet off the ground on a log no wider than his tires, barreling down a rocky chute at 30 miles per hour, or, if you look up, flying through the air at about the height of your head.

What you’re seeing is the first ever urban mountain bike–skills park and the result of more than five years of work by the Evergreen Mountain Bike Alliance (formerly the Backcountry Bicycle Trails Club), the City of Seattle Parks Department and innumerable financial donors and volunteers.

The man responsible for the construction is I-5 Colonnade project manager Mike Westra, who I managed to pull away from a handful of diligent workers on a Friday afternoon in late August. The mid-September grand opening of the park was just over two weeks away, and while the Limestone Loop section of the park has been rideable since September 2007, Westra and his crew were working feverishly to have the park’s “core” features ready for the event. “This is the first in a new model of urban bike parks,” he said. “All the other urban bike parks out there, basically they found an existing park or green space, and they built trails in it. But this is land that’s packed with everything, from freeride, to pump track, to trails, to trials, to air, to beginner, to expert to everything you can get packed in a tight space.

“And, it’s under a freeway…right in the middle of a city,” he continued, as we toured the park while trying to avoid being run over by riders on mountain bikes so big and burly they looked almost like motorcycles.

The park is a maze of rock gardens, log rides, drops, and jumps, but Westra’s plan calls for terrain and features for all levels of riders. “Every feature at the Colonnade is built to exercise a particular skill,” Westra explained, pointing to the wider logs, smaller jumps, and generally more gentle features of the beginner-level trail. “I see these guys who started as beginners…and now they’re better jumpers than I am.”

As a cross-country mountain biker myself—the spandex kind—I’m certainly no authority on the type of freeriding the Colonnade is designed for, but the sections of the park designated “beginner” certainly looked less intimidating than the six-foot drops Westra had been showing me. With a penalty of falling only a few inches, as opposed to a few feet, this is where novice riders should focus their first efforts.

Before the city and EMBA started working on the park—which, along with the two-and-a-half-acre bike-skills area, includes an off-leash dog area, public art installation, and walkway that reconnects the long-divided Capitol Hill and Eastlake neighborhoods—the seven-and-a-half acres of land under the highway looked like what most people would imagine land under a highway to be. Simon Lawton, a professional mountain biker and owner of Seattle’s Fluidride bike shop, was the first to imagine building a park in the area, which he originally thought a “total wasteland.” However, he quickly saw the potential of the space. “It was kind of gross and kind of scary,” he chuckled when I reached him at Fluidride. “But I’m a downhill mountain biker. I look at any area that has vertical and think about what I could do there on my bike.”

Thanks to Lawton’s vision and the work of EMBA and its supporters, the I-5 Colonnade is now a clean and scenic Seattle park. But it’s hardly quiet. “Every once in a while you get a, ‘Why would anybody want to ride under a freeway?’” admitted Westra. “But most people think it’s so cool. Nine times out of 10—maybe 99 out of 100—they go, ‘Wow, what an awesome use of space.’”

“Awesome” is a word you hear a lot around here. “I almost stopped mountain biking, just ’cause it’s really hard to get out into the hills and ride,” said UW graduate student Donovan Power, one of the more skilled bikers we’d earlier been dodging. “But, lately I’ve been out here once or twice a week. It’s awesome. It’s totally awesome.”