Transcript for Mongol Derby: World's Longest, Toughest Horse Race
Well -- the only derby you've ever heard of takes place in Kentucky. Forget everything you know about racing horses because tonight we're taking you to the far reaches. Of outer Mongolia to one of the toughest races of any kind in the world. 850 horses over 600 miles and thirty extreme riders mostly women. In the adventure of their lives they say if -- can complete the mumbled derby you can do anything. And our special edition of Nightline sends correspondent Gloria Riviera and producer Alex water field to join the -- Need is a race like no other six companies -- unfunded. We're -- Warner wind up with the -- coming out of the last station laugh honey B aren't. Campaign -- now. Next hearing at high speeds across the wilds of outer Mongolia. Here -- -- thirty streaming -- jurors who are attempting to fears among gold derby. And for the first time ever most of them are women and. We came here to find out ladies it drives them put themselves through this. And what it takes me. All in the under the pillows on the -- on the news. And little moment. We meet the racers here. In the remote Mongolian -- You eight -- Heidi -- I'm very proud of fuel the -- pre race ritual organizer Katie -- is a bullet Eric. A -- -- cocktail and fermented horse now. Tighten your gas and provided like -- so that's my roommates -- Street. Experiences of my blood my father's an alternate. Yeah. First there's -- who -- Twenty year old hotshot from Houston convinced there is only one reason to be here with -- -- you know in this thing yes. I don't believe that's the plan the plan but is weak and -- it would soon learn. It's not about winning or even surviving -- OK it's about surviving but it's about something much more. To everyone and their hours. There's -- a lifelong equestrian. Fifty -- she's one of the oldest contestants. As a secret reason for attempting this race. It had something. I haven't been. They feel comfortable K. I'd bet that share after -- And news talk friendly 23 year texting college grant. Recently entered the workforce because he -- equivalent crisis -- actual title as a risk management. And you're out here yet he not analyze -- and -- -- when the Atlanta as -- -- she. But -- a little too much -- throws off time. Condoleezza. -- -- -- -- I think -- published an analyst at times seems to injured his shoulder and handling the needs of -- -- She. Sixty M race -- dent in his first up and ready to go this other riders make their final crafts and mayor Eddie. I haven't made any clients and their promises derided they keep up let -- -- -- it is start. -- -- using a different strategy teaming up with the -- -- -- Sandra to ride together. -- is still dealing with the aftermath of last night and Texas how about a man. According to -- and personally its procurement specialist but he grits his teeth and saddles up. -- local -- of them when you. Final blessing my greatest moment. -- -- -- It's just time. -- -- -- -- -- There is no marks trail near upset how. Writers have a crude map to GPS from their guts tonight. Over the next few days able to charge their way through 25 check. Teaching courses in each one covering at least two marathons each day -- their 620. Mile journey. Lucky for us -- team has a different -- of -- power to get ahead of these extreme writers. And seven from day one DeVon has -- -- Start -- a single person. She gets first pick of the new sources programs -- GPS and his -- The rest of the pack starts to -- Including Clark's career homers and Michael. -- -- Duncan is and I'm. -- This any nineteen year old bridge is turned off by DeVon has revised its -- investor. You think -- he would -- -- if I didn't finish in seven days I'm not going head. Then comes not blocking -- -- that bum shoulder now a real problem. It was most comfortable ride -- remembered -- -- and -- on that there is more bad news. 76 -- amendments that are need to move it -- Each station event. Performs a thorough check up on each riders horse the first thing -- is the hot trades it needs to be. 64 -- and 64 besides a statement contestants are given a tying penalty if their forces arresting Murray is too high. I'm -- Maybin overworked. Tom's group won't -- for. He doesn't want to -- alone. You get caught out by yourself. At night. And you lose your -- here literally middle of nowhere I don't know who helped. Still sticking together and -- and Sandra -- becoming fast friends. London this is our home between stations they decide to stay the night in the home -- local Mongolian you know -- The next morning but. We -- -- -- -- to all smiles and ready ago when he did not. We're starting to discover that her rosy outlook actually makes her -- fears and -- at. Beyond headed straight out yeah. -- I didn't I -- way. Some forty miles ahead. Forgetting is still so. Me. The incompetence. It's probably what -- -- -- Company and I'm here right here right okay. A major he's leaving because DeVon she's had some drama just -- the rivalry is developing between her. And I writer hot on her trail -- from the UK. And are amazed to find alarm -- first. It's just after 8 PM she only -- minutes of -- -- lessons for the daily duties had a car why not spend the night here tonight. And only time. There is now a competitive extradited perky persona this UK averse USA. Sending him and you can't passes Texas. -- -- -- -- -- -- We've learned sadly have to leave we see -- admitted that threaten around -- -- -- -- -- -- -- that -- -- you look through these. A little bit -- -- To our surprise we -- -- -- she does -- only teaching her go it alone monster about it chancellor either there's tons of every other. That's a different strategy for which -- it doesn't. I've got to play. But once friendly -- -- interested in the offer or it seems even acknowledging her rival at all. With ten minutes. I just about how -- should get at twelve minutes and why would she leave with woman. I'm just read to me hand. Seven Bob got -- fix comes his way. It's kind of content sources spending the night there is definitely making a -- comments. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- this is left writing 200 miles despite this searing pain in his shoulder. And yet another -- -- -- So -- again. My horse Thursday option and took -- back to the beginning of her. Tom fine his source -- alone again he decides enough is enough. That we never have this conversation. It's a thank you -- make it. Such. Lessons learned. How to wrestle mongolians before the sort of 600 -- -- -- -- Tom becomes the sixth the writer to quit the race. And it looks like -- maybe next. -- -- -- -- together this whole race may now have to split up. -- It needs to convince companies to -- When we come back with only two more days ago we might get an aunt -- you -- now throwing out. Pounding finish -- shock. Only god.
This transcript has been automatically generated and may not be 100% accurate.