Just 60km off Perth, the sea floor plunges into a dark gorge, as wide and deep as the Grand Canyon and more mysterious than the surface of the moon.
But from this weekend, a group of acclaimed WA scientists hope to become the first to learn its secrets on a deep-sea expedition aboard a research "super ship" donated by the multibillionaire head of Google.
For the first time, the scientists will explore the steep walls of the Perth Canyon using a remotely operated vehicle, potentially uncovering new species and gathering invaluable samples.
Professor Malcolm McCulloch, a coral expert from the University of WA, is the chief scientist for the 12-day mission. It will also include 11 other scientists, from UWA, the CSIRO, the WA Museum and Italy's Institute of Marine Sciences.
The Perth Canyon was "a great unknown" and provided a genuine new frontier, Professor McCulloch said, but that uncertainty made the work too expensive and risky for traditional funding sources.
So he put forward a proposal to the Schmidt Ocean Institute, a philanthropic science organisation set up by Google executive chairman Eric Schmidt and his wife Wendy. The institute operates the RV Falkor, a research vessel that has had a $120 million refurbishment and is now available at no cost to selected scientists around the world.
The institute "loved" the Perth Canyon proposal, choosing it from many applications to be one of just eight projects it will support this year.
The Falkor and its crew, including specialists to operate the ROV, arrived this week from Tasmania on its first trip to WA.
After the Perth Canyon expedition, the ship will take a separate group of scientists to do research on Scott Reef, off Broome.
After the Falkor docked at Henderson, the crew loaded a hired ROV, believed to cost up to $100,000 a day.
Professor McCulloch said the cost alone would put it "out of the reach of scientists" under normal circumstances.
On Sunday, the ship will leave for the Perth Canyon, honing in on areas that appeared on previous sonar scans to be the most likely to yield something interesting.
The canyon was formed over tens of millions of years, when the area was the ancient mouth of the Swan River.
Professor McCulloch said there were probably mountains in the area at that time, so the river ran so strongly that it cut deeply into the earth. When the continent subsided and the seas rose, it formed an underwater abyss up to 4.5km deep.
Today, the ocean above the canyon is a global hotspot for marine life, where nutrient-rich waters well up from the depths during summer and autumn, attracting whales, sharks and other marine life.
But the canyon itself remains mostly unexplored.
Sonar mapping had given a sketch of its shape and some clues had also come from dredging samples and photographs taken up to 500m down. But the ROV would give an unprecedented insight into the world that existed at the more inaccessible depths, Professor McCulloch said.
One of the goals of the mission is to determine what lives in the lower reaches of the canyon, as well as on its walls.