It is fascinating what our bodies are capable of once properly trained and conditioned. Last month I completed my first full marathon, 26.2 miles in my home city of San Francisco. Although a great personal accomplishment, at the end I felt unchallenged and therefore somewhat unfulfilled. There has to be something more, a race that would push you to your absolute limit. This is a list of some of the most challenging races in the world.

“The will to win, the desire to succeed, the urge to reach your full potential … these are the keys that will unlock the door to personal excellence.” – Confucius

10. Great Wall Marathon

• This event is widely acknowledged as one of the most challenging marathons in the world. Elevation, heat, and poor air quality are all factors runners must overcome as they go up and down the “5,164 steps into history.”

9. North Pole Marathon

• This is the “World’s Coolest Marathon” and is also the northernmost marathon on Earth. Participants will battle against the extreme cold as they trek through 26.2 miles of artic terrain, individually or in groups of three.

8. Inca Trail Marathon

• This 500-year-old Inca trail passes through the Andes Mountains, going from Cusco to the ancient city of Machu Picchu. The average finishing time for this event is more than 10 hours.

7. Ironman

• This ultimate triathlon is my personal goal. Ironman consists of a 2.4-mile swim, a 112-mile bike ride, and a 26.2-mile run (full marathon). There is a 17-hour time limit to complete these three events. This event is widely acknowledged as one of the most difficult one-day races in the world.

6. HURT 100

• The HURT is a 100-mile race that winds through the Ko’olau mountains of Oahu. The course includes thick jungle brush, rocky streams, heavily rooted trails, and a cumulative elevation gain of over 24,500 feet. Runners have 36 hours to complete the 100 miles.

5. The Jungle Ultra

• Runners manage their way through 142.6 miles of the jungles in Peru. Although mostly downhill, runners battle temperatures more than 90 degrees fahrenheit with extreme humidity and are also faced with unforgiving terrain with a variety of insects throughout.

4. Plain 100

• With just more than 100 finishers since the event started in 1997, this 100-mile race is one of the most difficult on the planet. Plain takes place on the remote backwoods in Washington and emphasizes that the runner receives no outside aid.

3. Badwater

• Described as “the world’s toughest foot race,” this ultramarathon covers 135-miles through the hottest place in the U.S., Death Valley. With temperatures reaching more than 120 degrees fahrenheit, only one hundred brave souls participate each year.

2. Iditarod Trail Invitational

• Following the famous Alaskan 1,000-mile Iditarod trail from Knik Lake to Nome, this race can take up to a month to complete. Day and night participants bike, ski, and walk through the cold wilderness.

1. Self-Transcendence

• Although one of the most boring, repetitive races, it is also the longest at 3,100 miles. Runners must complete a daunting 5,649 laps around the same block in Jamaica, Queens, New York. This usually takes runners upward of 50 days to complete.