Courtesy of Sarah Outen

Sarah Outen has never been one to shy away from an adventure.

Since 2009, the 26-year-old has rowed solo across the Indian Ocean, biked through the Gobi desert, and kayaked and cycled from the edge of Russia to the tip of Japan's main island in just five weeks. Along the way, she's come face to face with bears, fought off snakes, braved shark-infested waters, and turned down three marriage proposals.

Now Outen is ready for what could be her biggest adventure yet - a solo row across the North Pacific Ocean.

"I love setting myself up for a challenge and all the things that come with that," Outen told ABC News. "It's the discovery, the satisfaction of really testing yourself and finding out how far you can go."

The journey, which she plans to start Friday, will take Outen from the east coast of Japan to the west coast of Canada, a trip that is expected to take 150 days, and cover 4,500 miles. If she's successful, Outen would become the first woman and only the third person to complete the trip.

The solo row is part of a larger 20,000 mile, two-and-a-half year journey around the world that Outen began in London, a year ago. Dubbed "London2London: Via the World," the trip is an attempt to tackle two oceans, three continents, and 14 countries, using human power alone.

The British adventurer says the idea for the journey came to her while she was rowing from Australia to Mauritius three years ago. That trip - which she was the youngest person to complete - was inspired by her late father, who died in 2006 after a long battle with rheumatoid arthritis.

"Seeing my father suffer so much really showed me as a teenager how life is short," Outen said. "You've got to make the most of it right now, because you don't know what will happen tomorrow."

After completing her Indian Ocean row, Outen returned home to Rutland, England to begin hashing out her global adventure, while working as a motivational speaker and writing a book about her trip.

She says she mapped out the first half of her trek by drawing the straightest line she could - given weather issues and visa requirements - from London to Japan. Outen set out from the Tower Bridge last April, with little more than her 16 foot kayak, "Nelson."

In a span of eight months, she kayaked down the Thames, across the English Channel to France. She cycled 10,000 miles through France, Belgium, the Netherlands, Germany, the Czech Republic, Poland, Ukraine, Russia, Kazakhstan, and China, before taking on Russia's Far East.

She kayaked 1,000 miles from the remote Russian island of Sakhalin to Japan, where she has been training for the Pacific Ocean row, for the last four months.

Outen has traveled alone a majority of the time, but she's had some company along the way, thanks to unexpected encounters.

At a gas station in China, she met a young man named Gao, who was so intrigued by Outen's journey, he decided to join her on the spot. He bought a bike that day, and pedaled nearly 2,500 miles across China, for 35 days.

"He was scared, he was worried, he didn't know if he would make it," Outen said. "But every day we just hit up the problems with solutions, a laugh, and a positive attitude."

Outen has documented every step of her journey on Twitter, and has been writing a daily blog. She's chatted live with schools around the world, with the help of a dedicated team of supporters back home that includes a media relations person, an accountant, and psychotherapist.

The group also helps tracks weather conditions and makes sure Outen stays on schedule, something she says was especially helpful during the trek across Russia, the toughest leg of her journey so far.

"If you think about it, I'd been cycling for five-and-a-half months by the time I reached the edge of Russia," she said. "To suddenly get into a kayak was a bit mindboggling. We were also under a lot of pressure to get that phase done due to visa restrictions and weather windows."

Outen said she knows there are bigger hurdles ahead.

Courtesy of Sarah Outen

To prepare for her lone five-month trip at sea, she has built a customized 21-foot solar-powered boat, and stocked it with seven months worth of food, a first aid kit, boat repair equipment, and every communication device imaginable. She has equipped the vessel, named Gulliver, with a desalination unit that makes saltwater drinkable.

"It could easily be frightening. There could be waves, I could capsize, I could run into ships, there's all sorts of dangers," she said. "The energy, the drama, and the close encounters with wildlife will definitely trump all of that for me."

Beyond the sense of adventure, Outen has a larger goal: to raise more than $160,000 for four charities, she says are close to her heart.

If Outen completes her Pacific Ocean row, she will still have to cycle 3,000 miles from Vancouver to Nova Scotia, and row an additional 3,000 miles to reach London.

For now, her eyes are set on the water.

"It's just me and the boat [for the next five months]," she said.

To follow Sarah Outen's adventure, visit her website.