When Beverly and Peter Pickford decided on their most ambitious project to date, their vision was of such magnitude that it took a while for them to define the parameters.
The idea was to capture the world's last wild places. But what criteria would these destinations need to meet to qualify?
One of the things they agreed on was that these lands had to be of a scale that they "evoked fear and reduced humankind to humility".
Then how to identify them. As a starting point they used Google Earth at night as a tool to pinpoint places that had the least light and were thus the most remote locations.
The result, four years and all seven continents later, is Wild Land, a breathtaking work of photography and discovery.
The South African couple, who have been wildlife photographers for 35 years, sold their beloved farm in the Cape to help fund the book. Peter writes about how his younger self decided not to pursue the family occupation of medicine and instead he "stepped out the back door into the fields and sunshine". He never looked back.
On their odyssey they were exposed to extremes: from the murderous heat of Namibia's Skeleton Coast to the frozen peaks of Tibet and Patagonia.
In Antarctica these extremes reach their peak with ice up to 4.8km deep in places - in what is the driest place on Earth. It's also the coldest, with recorded temperatures of -89.6°C, and the windiest, with winds of up to 320km/h.
On the Tibetan plateau Peter encountered a lone shepherdess in a traditional cloak embroidered in blue and red, dwarfed by a desert where no trees interrupt the landscape.
Their 200 photographs also illuminate and highlight a myriad forms of life, among them polar bears, desert elephants, the yak and king penguins.
Underpinning their work is a powerful message about the state of our planet and our inability to see beyond our own lifetimes...