The Mega Cavern mountain bike trails will open in January, 2015, with 12 miles of trails.

Located underneath the city’s outskirts, the aptly named Louisville Mega Cavern will be the first underground trail system in the world. Built over 350,000 square feet – picture two Costcos side by side and packed with dirt and stone – the beginner- to expert-level trails were planned by trail designer Joe Prisel and built by a small army of local volunteers.

“When the [Mega Cavern] operators first approached me, my first thought was, ‘How are we going to fit this inside a cave?’” said Prisel, who also designed and runs the recently-opened Burlington Bike Park in Washington state. “But then I saw how huge the caverns were with their 90-foot ceilings. It’s so big, it feels like you’re outdoors.” 

Because the caverns are man-made with no real natural features to speak of, Prisel was essentially given a blank slate. Prisel made his name designing bike parks for ESPN’s X Games, and a quick ride through his newest creation showcases those influences. Most indoor bike parks like Ray’s in Cleveland and Milwaukee rely on wood structures and obstacles to simulate the outdoors, but the Mega Cavern has long been a dumping site for local construction fill, giving Prisel plenty of dirt and rock to play with.

A massive BMX-style jump course is the prize of the bike park thus far, with riders soaring off the steep tabletops, nearly touching the cavern’s ceiling. With enough momentum, riders can launch themselves onto a series of mounds atop an old shipping container, then drop down back onto the trail.  

Riders who prefer to stay closer to the ground will delight in the flowing, bermed turns that allow them to get nearly horizontal as they build speed. The singletrack alternates between fast, wide-open trail with some rock jumps and incredibly tight pathways to test technical skills. A pump track section will teach riders how to best transfer their momentum into speed.

Looped together, the trails offer about 12 miles of jumps and singletrack, assuming you hit each of the different lines. Park staff anticipate only 10 percent of the trails will be considered black-diamond level, with those obstacles – mostly rock gardens, jumps, and drops – including a ride-around option. That way, Prisel said, friends and family members can ride most of the same trails, despite differences in skill level. 

The trails offer enough variety and challenges to keep riders at the edge of their saddle for several hours. Prisel designed the course with short-travel cross-country bikes in mind, but any knobby-tired rig will do. The lack of elevation also makes single-speed rigs ideal. 

As December rolls to a close, the cavern trails are about 85 percent completed, with a wooden bridges and obstacles to be completed before the late January opening. Next up, Prisel and company will begin work on an additional 50,000-square-foot jump park and riding school. A short-track racing series is already being discussed for 2015.

Thanks to the modular nature of the park, Alec Zaremba, Mega Cavern marketing associate, said that many of trails can be changed and rebuilt throughout the year, giving frequent visitors something new to ride. 

An even bigger boon: Because the former limestone quarry maintains a constant 60-degree temperature throughout the year, the cavern owners see the trail as a go-to winter destination for riders not only from the Midwest, but also from around the world. Zaremba said that he’s already gotten inquiries from as far away as Australia, and a European cycling team training in the area stopped by in November for a quick preview of the trails. 

If the underground trails are a success, Zaremba said there’s room for further expansion in the mammoth caverns. The cavern holds more than 4,000,000 square feet of space, with only about a tenth of it in use for the trail.

The owners are still ironing out details ahead of the opening, but visitors can expect half- and full-day passes, rental bikes, and, eventually, a small bike shop for repairs.

Watch a drone flyover of the BMX trails.