Nichola Bennett (31) is half of a tandem cycling team that will ride about 1600km from John O'Groats, Scotland, to Land's End, England, over 10 days next month.
Her cycling partner, Julian Heitz, is blind.
Ms Bennett will be his navigator and early-warning system on a journey that had opened her eyes even before it started.
"We've already done a lot of training, and it's shown me that there is so much more to appreciate out there," the former Columba College and Dunedin College of Education student said from London recently.
"I can tell Julian about the potholes and the traffic, but he tells me about the smells of the trees and the flowers, and about the sounds I probably would never have noticed.
"It's been wonderful."
Ms Bennett taught Mr Heitz's daughter at The Village preparatory school in northwest London, where she has been a sports, mathematics and English teacher since arriving in England six years ago.
She became a family friend, and was soon Mr Heitz's tandem cycle sidekick.
The fundraising ride seemed a natural progression: Miss Bennett has already run the London, New York and Milan marathons for charity.
Last week, barely a month from her current challenge, she tentatively agreed to again run the New York Marathon.
"There's something amazing about doing something that pushes you but also helps other people.
"I really enjoy being engaged in physical activity, but this is giving it much more of a sense of purpose."
Marathon training on the nearby heath was a solitary, physical experience, but tandem bicycle training was also mentally tiring.
The pair train 15 to 20 hours a week, and cycle about 160km each day they ride.
Ms Bennett sits at the front of the bike and has to tell Mr Heitz about everything on the road ahead.
No vehicle, turn, pothole, roundabout, judder bar, or traffic light can be left unspotted, and no warning can be left too late.
"I knew I'd be physically exhausted at the end of a ride, but I am also surprisingly mentally exhausted.
"I have to be aware of everything. Missing anything could mean getting hurt."
As drained as she might be, Ms Bennett - whom Mr Heitz calls an "energy-filled mobile nuclear reactor" - was looking forward to the challenge of 10 tiring days cycling and seeing so much English countryside.
"But I guess the real success will be raising as much money as we can for the National Blind Society. And actually completing the ride."
