Ultra marathons are races that go beyond the traditional 26.2-mile distance of a marathon. They can range from 50 kilometers (31 miles) to 100 miles or more. These races are not for the faint of heart, and require a significant amount of training and preparation.

One of the most famous ultra marathons is the Western States 100-Mile Endurance Run, which takes place in California's Sierra Nevada mountains. This race has a reputation for being one of the toughest in the world, with over 18,000 feet of elevation gain and loss over the course of the race. Another famous ultra marathon is the Badwater 135, which takes place in California's Death Valley and is known for its extreme heat and challenging terrain.

If you're interested in learning more about ultra marathons, there are many resources available. Books like 'Born to Run' by Christopher McDougall and 'Finding Ultra' by Rich Roll provide firsthand accounts of what it's like to run these races. Additionally, websites like UltraRunning.com provide information on upcoming races and training tips for aspiring ultra runners.

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