This ladies-only event is making its debut with a splash—and a run, jump, and climb. It’s an obstacle course that’s designed to test speed and cardio as well as more general components of overall fitness like balance, strength, and agility. Mazes, ropes, and some surprise elements will block women from the finish line, with prizes awarded to the top three finishers in each age division.

Step up to fight cystic fibrosis. Participants climb the 3,856 stairs at Sports Authority Field at Mile High in order to raise money and increase awareness of the Cystic Fibrosis Foundation. Take the stairs at your leisure, or run a mile high for a leg-burning workout, but either way, the survivor party will be waiting at the top with food, drinks, and music. Sat 8 a.m.

Bike through Denver looking for clues, doing as many wacky tricks as you can, and trying to outsmart your competition. There’s an inflatable slip-n-slide, mystery checkpoints, and quizzes that guarantee the winners aren’t just the fastest—but also the most clever.

Colorado Youth At Risk, which focuses on transforming the community through relationships between youth and their mentors, is holding a race to showcase some of those relationships for the second year in a row. The organization helps high school students graduate with the help of an adult mentor, and it needs support from the community to keep spreading the good.

Mountain bikers enjoy 30 miles of trails, live music, and Avery Brewing Company beer, all while fundraising to benefit the National Sports Center for the Disabled and the American Red Cross. There’ll be on-site adaptive cycling clinics to teach skills necessary for handcycles, tandem bikes, and therapeutic tricycles for both kids and adults.

Would you run faster if you were being chased by zombies? This race combines a 5K with a game of flag football, an obstacle course, a maze, and the undead. Runners will have five “health” flags, which the zombies have been trained to go after, and if you run out, you’re dead. Or your chances of winning are, anyway.

There are adventure races, and then there are mountain biking, running, kayaking and navigation races like this one, built to challenge the most seasoned adventurer. There are two different courses, the sprint course with around 26 miles, and the sport course with around 53 miles, that will test physical strength and mental stamina.

Grab a teammate and get ready to participate in a city-wide scavenger hunt for the chance to win $10,000 cash. Drive to various checkpoints in Denver's neighborhoods—ranging anywhere from open homes to hardware stores—to find clues and perform challenges for points. The team with the most points will be crowned winner at the post-race party, which will have food, drinks, and prizes.

Participate in an hour-long spin class to help disabled athletes. Every hour, the FORZA Fitness and Performance Club will be offering spin classes to riders of all skill levels who wish to benefit the National Sports Center for the Disabled. All day, there will be a chance to participate in a silent auction.

During the day, these roller derby athletes are moms, students, and professionals, but at night they unleash their fierce competitive side. Find out why roller derby is becoming one of the fastest growing sports in America as you watch Denver's premier roller derby league, the Denver Roller Dolls, take on their rival, the Rocky Mountain Roller Girls. Sat 7 p.m.