For most people one Great Walk is achievement enough, but runner Romain Groleau had bigger plans.

Starting his journey on 28 December, Groleau ran all 10 Great Walks, crossing the finish line at 2am on Sunday.

The 44-year-old covered the distance of over twelve marathons, raising money for the New Zealand Nature Fund.

Originally from France but now living in Auckland with his wife and three children, Groleau told RNZ's Summer Times his body was holding up pretty well after his Herculean effort.

"I'm still a bit tired and recovering from the big effort and going back into the real world. I was a little bit disconnected for these nine days I was on the trail, so reconnecting and recovering."

He completed the Rakiura, Hump Ridge, Milford, Routeburn, Kepler, Paparoa, Heaphy, Abel Tasman, Tongariro and Lake Waikaremoana in eight days and 16 hours.

The weather was kind to him, he says.

"I had a little bit of rain on Milford and on Kepler, but we had a great weather window, and when we did Tongariro it was between rain and snow the period of time that we were running."

Lack of sleep, he says, was the main challenge.

"You run the trail and then you travel to the next one, and you need to keep on schedule, I probably slept less than five hours a night.

"So that was tough. And then the logistics, getting from one trail to the next, some of them require quite a bit of travel because they're not close to each other."

Groleau, who is vegan, had to ensure he had plenty of fuel onboard to keep going.

"Lots of sugar that would be coming from honey, from jam… but what I realised as well is, after five days, the body and the stomach wasn't really keen to take on more just sugar and sweet things.

"So, I moved on to prepared sandwiches, I'd stop at a bakery and buy specific sandwich that were vegetarian."

Prior to the challenge, he got plenty of kilometres in the legs.

"I run every day, for the past five years, I haven't missed a single day of running. So that gets the mind and the brain as well in the mindset of not stopping and continuing and running all the time.

"And I would run about 4000kms a year in general. So that's a lot of volume, and I do a lot of races, like ultra-marathon races, which also helped me to prepare for this. This year I did four ultra-marathon races, and with training of about 80km a week."

Romain Groleau's marathon effort will raise money for the New Zealand Nature Fund. Photo: Romain Groleau

Despite the physical stamina needed to complete the 10 walks, he had moments when he was able to marvel at the scenery, he says.

"Tongariro, the last one I did, was very special. I did it with a friend and we had this magic weather window, where the weather was super clear. We had this very starry sky, and just stopping in the middle of the night, it was close to zero degree at the time, and just looking at this sky and seeing the millions of stars, it was a bit like time stopped for a second."