When training for a marathon, there's a lot you need to take into consideration. You need to make sure you follow a specific diet, stretch properly, remain hydrated, and work out the proper muscles, along with other physical demands. One of the most crucial elements that many marathon runners fail to take into consideration before their first big race is the psychological training. You can be as fit as possible, but if you're not mentally prepared for a 10-kilometer run, you could find yourself slipping behind simply out of subconscious boredom. Of course, boredom of any kind is the absolute last thing you'll be experiencing if you instead opt to tackle OCR. OCR – or "obstacle course racing" – has taken the marathon world by storm with its breakneck pace, onslaught of physical challenges, and emphasis on completion rather than competition. Millions of thrill-seekers across the globe jump at the chance to experience one of these races, and most of them are more than eager to come back for more. What exactly is it that drives people to throw themselves into mud, wade in buckets of ice water, or even get zapped by electrodes for 10 miles for fun? Read our list of the six best obstacle races out there, and we'll let you decide (you may want to grab a towel)!