The sky is that sullen lead colour only an artist could love. Here's two of them: Mombassa (aka Chris O'Doherty) and his daughter Lucy O'Doherty, walking the coastal path from the empty carpark at Garie Beach to the clump of shacks on the hill, in the Royal National Park, more than an hour south of Sydney.

There's no bitumen here. No phones. No coffee carts. "There's no roads, there's no telegraph poles. It's a little bit different from the normal suburban beach," Mombassa says. "Considering you're so close to the city, it's kind of isolated."

There are about 140 shacks in the heritage-listed cabin communities of Little Garie, Era and Burning Palms. Their unlikely survival is celebrated in the exhibition Shack Life, part of the Australian Heritage Festival program of more than 1000 events across the country.

"It is a nice, timeless, unchanging place, really," Mombassa says. "The waves and the wind and the birds."

His wife Martina's family have shared a single-room shack at Era since the 1960s, accessible only by foot along a 40-minute beach path or steep bush track. But Mombassa's dodgy ankle stops us short at Little Garie.

At "The Sugar Shack" on the hill, among the sea scrub, we meet Yamba sugar cane farmers Tim and Denise Strange. Sitting outside their green-and-blue shack, by a farting dog T-shirt drying on the clothesline, are strange sculptural creatures created from flotsam washed up on the beach - snorkels, construction-site helmets, baseball caps, plastic babies. "They're the watchers," Tim says.

Inside the shack, which his father built in 1937, are makeshift mobiles of dried seahorse skeletons and sea urchins. We sit at the kitchen table by a wall of wine corks. Mombassa is wearing a black beanie, black jacket, black jeans, black boots and a badge on his left lapel of a unicorn vomiting a rainbow. O'Doherty has a jangling skeleton on her shirt.

Hanging on a wall of their own shack is a banner of Mombassa's illustrations for Sydney's 2013 New Year's Eve celebrations, of all-seeing trees and one-eyed koalas. Scattered around are the small driftwood sculptures made by various cousins.

The Shack Life exhibition, at the Hazelhurst Regional Gallery & Arts Centre, features the works of established artists and members of the shack communities. Something about the shacks seems to agitate artistic inspiration. Margaret Olley, Max Dupain, David Boyd and former Art Gallery of NSW director Hal Missingham are among those who have spent time in the small communities.

O'Doherty, winner of the 2016 Brett Whiteley Travelling Art Scholarship, likes painting pictures of the small structures, which were cobbled together between 1910 and 1950, many of them during the Depression. "They are simple buildings but also quite strange, when they're made of second-hand materials," she says.

"I like the way they nestle into the bush so nicely. It is like they have always been here. Someone once said they look like bits of driftwood washed in from the shore and that have kind of settled here."

One of her earliest memories is lying in bed in their shack as a small child and listening to rain terrorise the corrugated iron roof. "It's very Australian," she says. "Beautiful but with a sense of danger as well."

Mombassa recalls leeches slavering on the windows. A brown snake on the front doormat and a wallaby by the back door. He once had to flee a big grey kangaroo that wandered inside. One night, he was woken by the sound of a possum gutsing on fruit at the kitchen table. "You can't keep the wildlife out of bush shacks."

He packs an A4 sketchbook for short stays at Era. "I have done a lot of drawings of the headlands, the shacks, the bush. Or night drawings of the moon or the goings on at the surf club," he says. "Anywhere you look is something interesting. There is a great big gum over the shack that I hope doesn't come down on the house and flatten it. The patterns in the bark and the limbs are like humans'."

O'Doherty says the isolation from everyday distractions helps her concentrate and relax. "You lose a bit of city anxiety when you come here," she says. "It's just a simple way of living, it's very energising. You spend hours on drawings but it doesn't feel intense because there is nothing else really to do. You're not going anywhere, you're not going to watch TV."

Time becomes irrelevant, I say. "Yeah it does," she says. "It's really nice not having to pay attention to time."

Our time is up. Mombassa has a meeting back in the city and steels himself for another shuffle along the narrow beach track towards the real world. He glances at the churning buttermilk sea as we farewell Mr and Mrs Strange, and step outside.

"It's a $5 million view," he says.

"Don't tell anyone," Tim says.

The Shack Life exhibition is at the Hazelhurst Regional Gallery & Arts Centre, Gymea, until May 2, as part of the Australian Heritage Festival, which runs until May 21.