Whether it’s thermometer-busting temperatures, overwhelming distances, high elevations, fast descents or massive climbs, the following 24 races take competition to the extreme. Enter at your own risk and prepare to enter the pain cave. There are many other very challenging races we could have included on this list, but these epic events should be enough to get your heart racing.

PHOTOS: Colorado’s Hardrock 100

SUBSCRIBE: Get A FREE Subscription To Competitor’s Digital Magazine!

Loon Mountain Race, Lincoln, N.H.
7 Sisters Trail Race, Amherst, Mass.
Grand to Grand Ultra, Grand Canyon Village, Ariz., to Escalante National Staircase, Utah
Speedgoat 50K, Snowbird, Utah
Mt. Washington Road Race, Gorham, N.H.
Badwater 135
Badwater 135 runners won’t be starting at Badwater Basin anymore.
Bridger Ridge Run, Bozeman, Mont.
Barkely Marathons, Wartburg, Tenn.
Pikes Peak Marathon, Manitou Springs, Colo.
Grouse Grind, North Vancouver, B.C., Canada
Fat Dog 120, Keremeos, B.C., Canada
Mount Marathon Race, Seward, Alaska
Equinox Trail Marathon, Fairbanks, Alaska
Canadian Death Race, Grande Cache, Alberta, Canada
Mount Mitchell Challenge, Black Mountain, N.C.
Catalina Island EcoMarathon, Catalina Island, Calf.
Chuckanut 50K, Bellingham, Wash.
Haleakala Run To The Sun, Maui, Hawaii
Grandfather Mountain Marathon, Boone, N.C.
Wasatch Front 100 Mile Endurance Run, Midway, Utah
Blue Ridge Marathon, Roanoke, Va.
Leadville Trail 100, Leadville, Colo.
Yukon Arctic Ultra
Hardrock 100 Endurance Run, Silverton, Colo.