Jill Heinerth didn’t get to live her childhood dream of becoming an astronaut. Instead, the Torontonian has dedicated her life to exploring a different sort of alien landscape: the world of underwater caves.

Heinerth gave up her day job as a graphic designer before she turned 30 so she could devote all of her time to exploring almost inaccessible and undiscovered environments. Now 55, she has dived the world’s longest, deepest and narrowest caves, including an iceberg in Antarctica – a list of achievements that will see her inducted into the International Scuba Diving Hall of Fame this year.

There is no greater thrill than diving in a place where no human has ever been

Jill Heinerth

It’s incredibly risky squeezing your way through narrow, pitch-black underwater caves. The slightest mistake could end up costing you the ultimate penalty – in an average year, as many as 20 cave divers lose their life.

But Heinerth says the counter to that risk is exhilaration. “There’s no greater thrill than diving at a spot where no one else has ever been,” she says. Heinerth admits that even with years of experience she still gets scared, “but you can’t let it take over, or else you’ll use up too much air”. So, how does she cope with high-risk situations? “Take a deep breath when you come face to face with danger,” Heinerth says. “Then take a step-by-step approach to what you need to do to survive.”

Call of the unknown

Deep thrills

© Jill Heinerth

In 2000, Heinerth had an accident in this cave – the Pit, far below the Mexican peninsula of Yucatán – that almost brought her career to an end. But the Canadian says that the thrill she gets from diving outweighs any risk.

Hidden wonderland

Spellbound

© Jill Heinerth

Visiting this bizarre underwater landscape off Bermuda requires a special permit, as the cave has been out of bounds for 40 years on safety grounds. “I have always been utterly spellbound by the beauty,” Heinerth says. “I think this cave is one of the most amazing things I’ve ever seen.”

The deepest desert

Dan’s Cave is believed to be 350,000 years old

© Jill Heinerth

Dan’s Cave, located deep beneath South Abaco in the northern Bahamas, is believed to be 350,000 years old. The underwater cavern is of particular interest to climate researchers, as deposits of sand blown by the wind from the Sahara and across the Atlantic have been found here. By researching the cave’s stalagmites, it’s been possible to determine when our planet has experienced periods of drought.

Tight squeeze

Claustrophobia becomes the new normal

© Jill Heinerth

Moments of claustrophobia such as this are par for the course for cave divers. To get through them, Heinerth says, you must “strike a balance between fear and self-belief.

Deep history

Exploring wrecks

© Jill Heinerth

This French ship was sunk by a German U-boat off Bell Island, Newfoundland, in November 1942. The wreck-cum-artificial reef is now home to a plethora of marine life.

Towing the line

The safety line is a diver’s only route back to the surface

© Jill Heinerth

Heinerth’s dive partner secures the safety line at the entrance to the Devil’s Eye Spring in Florida. This is the only way to ascertain where you are, should dislodged silt suddenly reduce visibility to zero, which is pretty common.

Divine light

A beam of light penetrates the depths

© Jill Heinerth

A ray of sunlight penetrates the darkness of a cave in Mexico, bringing to mind the Mayan belief that these karst caves were home to the gods of the underworld. “I call this picture from Yucatán ‘Beam me up,’” laughs Heinerth.

Strange brew

Rivers of tannic acid

© Jill Heinerth

The waters of the Santa Fe River in northern Florida are stained this brownish-red colour, which resembles tea, because of tannic acid released by decaying cypress trees.

American underworld

Obstacles wait for Heinerth down in the caves

© Jill Heinerth

The Floridan aquifer is a network of underground channels that branch out in all directions and provide groundwater to 60 per cent of the state’s population. It also has a magnetic pull for fearless cave divers from all over the world. This is the entrance to the Sunshine State’s Orange Grove Sink Spring.

Safety selfie

Heinerth wearing her rebreather

© Jill Heinerth

Heinerth tests a rebreather – a device that recycles the diver’s air, enabling longer explorations.