Still rowdy since 1989, the Thunderdown in the Underdown are grassroots mountain bike races in Northern Wisconsin. It’s conveniently located only 6 miles off of Highway 51 and offers racers a wilderness experience on challenging topography formed from glaciers that swept the area thousands of years ago. The course is primarily singletrack climbing hills (up to 75!) that pass by isolated lakes and dozens of boardwalks. The Thunderdown in the Underdown mountain bike race continues to be part of the Wisconsin Endurance Mountain Biking Series (WEMS) races.