LOUISVILLE, Ky. » It’s the perfect setting: millions of tons of dirt, plenty of space and an atmosphere that stays at a constant 58 degrees.

A new underground bicycle park with miles of dirt trails, jumps and stunt courses is being built inside an abandoned limestone mine in Louisville that has been recycled into a popular tourist attraction. The owners of the 320,000-square-foot park say it will be the largest indoor course in the nation.

"We have a very large area to work with," said Tom Tyler, who co-owns the former mine, now called the Mega Cavern. "You can’t duplicate it. Somebody would have to go out and dig rock for 40 years before they have what we’ve got here."

Tyler and the other owners started out using the mine’s nearly 1 million square feet of underground space as a dumping site for dirt and rock in the early 1990s, and later as a storage site for businesses. About five years ago they installed zip lines in a section of the mine and in recent years set up a drive-thru underground Christmas light show that draws long lines of cars during the holidays.

Two decades of dumping gradually built the floor up over time, and gave the owners plenty of earth to work with. Tyler said there were requests from visitors and bikers to build a bike park in the mine.

Looking around the vast space spread over five football fields, with dirt trails unfolding in every direction under a 35-foot-high ceiling, the course has the breadth and feel of an outdoor space.

Indoor bike parks like Ray’s MTB in Cleveland allow bikers to ride during cold winters, and Tyler said he expects the Mega Cavern’s park to be busiest in the coldest months.

The difference is the trails at Ray’s and other indoor parks are typically built with wood. Burlington Bike Park in Washington is all dirt, but it is much smaller than the Louisville park.

"The dirt is a lot smoother for the steeper jumps, which we really like," said Derek Fetko, a local rider who has been invited in to test out the course. "Plus, being able to ride on dirt in the winter, it’s just something we typically can’t do here in Kentucky, because the ground freezes and thaws, it’s just too messy."

Two course designers from Washington state, Joe Prisel and Jeff Perkins, were brought in and began designing the course in October. Prisel designed the Burlington course.

"We brought them in and said, ‘Here’s the canvas. Paint it the way you would like to see it done,’" Tyler said.

It has long smooth stretches for take-it-easy riders, steep jumps for daredevils and plenty of rocks and other physical obstacles to ride around and on top of.

The course is expected to open in March.

By Dylan Lovan, Associated Press