A woody torture chamber awaits those brave enough to line up in a new ultra running race north-west of Auckland next week.
The Riverhead Backyard ReLaps Ultra involves running a 6.7km lap over and over again, starting each hour, until the winner is left standing.
The leading contenders will aim to run each lap in about 50 minutes, get 10 minutes rest and refuelling, before heading off again. The concept originated in Tennessee, where last year's winner prevailed over 68 hours.
One of the Riverhead favourites should be Kim Allan, a 51kg, 50-something marvel who is New Zealand's wonder woman when it comes to these endurance nightmares.
Not that she sees it as a nightmare.
Allan, who recently moved from Tuakau, south of Auckland, to a small South Island town, revels in pushing herself past normal limits, on treks full of pain, hallucinations and eventually sheer joy.
As events have turned out, she may not line up at Riverhead next week, her move to tiny Cave — between Timaru and Twizel — one of the complicating factors. She has still to make a final decision.
At the very least, Allan will be there in spirit for what she describes as a journey into the unknown.
"I could easily have done 24 hours, but after that, my time would slow down, and that's when it would become very interesting," she says of the Riverhead ultra.
"That is why it is such a cool race. You've got no idea how it might play out."
Allan (Walker) was a jockey until 2002 and she was no slouch, riding 67 winners, including an impressive 29 in the 1990-91 season.
But while juggling life as a single mum of four kids and working as a corrections officer at the big Spring Hill facility near Meremere, she took up ultra running, having prepared for her first ultra by walking a half marathon.
It became far more than a passing interest. She hit the headlines about six years ago attempting to break the women's world record for running without sleep. It was mission accomplished at the second attempt around Auckland Domain, where she nodded off after about 86 hours and 500km.
Hallucinations were among her companions.
"The first time at about the 370km mark, I bent over for a moment and kind of dozed off and then found myself in hospital on a hydration drip," she says.
"I thought I was in Paris, part of an adventure racing team, and had let my whole team down. A nurse asked me about accident compensation, and I thought, 'oh, so cool, they have ACC in France'.
"While I was running, tree roots would become big waves of lasagne, and the black tar came out of the road markings looking like stunning, amazing Aboriginal art.
"I made everyone in my support team stop and look at it — I wanted to take photos of things that weren't there."
Eventually, the pain "blended into everything" and kind of disappeared as the mind worked its magic.
She says altered images tend to strike at night, when runners' headlamps and other light sources dance on objects such as trees.
While I was running, tree roots would become big waves of lasagne, and the black tar came out of the road markings looking like stunning, amazing Aboriginal art.
In Greece's 246km Spartathlon, trees started to look like clowns on the long empty roads.
"You think, 'nah, that's not right', shake your head a bit, close your eyes and focus," she recalls. "Once daylight comes, you are fine."
But in an Italian mountain race, she thought daylight might never come again.
Allan had already got through a checkpoint when the race was postponed because of rain, snow and ice. Alone and with no other lighting, Allan believed she was on the wrong mountain as hypothermia set in.
"I was honestly thinking I had made a bad life choice here, and wasn't going to come out of this," she says.
"I couldn't get my fingers to open the zip on my pack to get the emergency blanket. It was pretty scary. On the way down, I started falling on an icy track."
A little yellow first aid bivouac appeared, the occupants surprised to find that anyone was left on the mountain. After a few hours' sleep, she set off again in the morning sun.
What to most people would be murderous training runs sound recreational in comparison, if catching the train from Pukekohe to Britomart then running back to Tuakau is your thing.
"It was great because there are a lot of petrol stations along the way where you can get water and lemonade ice-blocks — they are the best thing out," she says.
On another occasion, she set off at midnight with a couple of supporters and ran from Tuakau to and up Mt Te Aroha. After 21 hours of running, she did allow herself the luxury of a ride home.
In all of this, she has visited a physiotherapist only twice, never gone anywhere near a sports psychologist, and had a coach — an Australian named David Eadie — for just three months, online.
Eadie give her precious advice, that time on feet is more important than distance and mileage when training, but self-sufficiency seems to be Allan's general rule.
If she does manage to line up at Riverhead, organiser Shaun Collins believes Allan can win it. Ultra running is a sporting arena where women beat men.
Last year's backyard ultra in Tennessee got a publicity push when a 33-year-old American named Courtney Dauwalter, who has competed in New Zealand, finished second.
Ultra running is dotted with man-beaters: they include the so-called godmother of ultra running Ann Trason, another American named Pam Reed whose non-sleep record Allan beat, and Jenn Shelton from the younger generation. In January, 35-year-old Brit Jasmin Paris became the first woman to triumph in the 431km Pennines race, expressing milk for her baby along the way.
Allan is not motivated in any way by a desire to beat men. She says women's advantages probably include lighter frames.
"I know men have a lot on as well but women fit training in around kids, meals, full-on life," she says.
"There's that mental toughness — you just get on with things and maybe that is in our favour. We have less muscle mass to carry, and it doesn't come down to power for a massive sprint at the end. There is a lot of mental stuff. I don't really know why, to be honest."
She admits it was tricky training and being a mum, and she would time longer runs for when her youngest was at football training.
She also laughs while recalling her kids suggesting: "Mum, you don't have to do a crazy ultra to go on holiday."
Her main advice for anyone taking on the Riverhead Ultra is to start putting on layers of clothing before the cooler air arrives. And novices beware of how the flickering light at night plays on the trees, and with the mind.
Ultra running is the ultimate when it comes to the power of the mind overcoming the limitations of the body.
Allan uses a simple mantra when the going gets tough.
"I tell myself it would be a total waste of time to give up now, that the previous 12 hours would mean absolutely nothing," she says.
"You will be angry and gutted that you pulled out, and you are still going to be sore. If you want it to mean something, you have to keep going."