The Kowalski Brothers trail builders began carving out undulating runs through the pine plantation at Greenhills more than 25 years ago.

When the fires razed the area in 2003, Alan Vogt - the Kowalski Brothers' head designer - said some mountain bikers "bought road bikes and tried to get over it".

It was not long before the Kowalski Brothers regrouped and began building trails in other areas of Canberra.

In the past eight years, the group has been far more active, building a network of trails through Kowen Forest.

In the last year they've built trails in the Zoo Pines, near the National Zoo and Aquarium, and have remediated illegal trails from Black Mountain in coalition with ACT Parks and Conservation.

The chance to return to the arboretum site was an irresistible one though.

"We're as excited as we could ever be about returning to this venue. We call it our ancestral home even though it's a totally different venue now," Mr Vogt said.

Over the coming weeks, months and years, volunteers will pick-axe and shovel their way up and down the hills to create shared paths based off a series of "planned points" developed by the National Arboretum several years ago.

It's intensely physical work and the "ultimate non-gym activity", Mr Vogt said.

"You certainly will get your exercise for the day at a Kowalski trail session, there's no doubt about that. There's often a lot of very weary, feeble people climbing back into their car or getting back on their bike to go home.

"The other appeal of helping to build these trails is you'll be able to forever say 'I had a hand in that'. There's something really nice about knowing that you contributed to the canvas that is the trail network in Canberra."

You can sign up to build mountain bikes trails with the Kowalski Brothers' volunteer group here: selfpropelled.com.au/kowalski-brothers/get-involved