And down they go into unexplored waters. Pulling themselves through cracks and narrow passages to see a corner that nobody has ever seen, a sight unknown. Chasing that special feeling of being the only person to witness what you’re witnessing. These are the cave divers, the explorers who choose passion over risk to see what lies in this quiet, undiscovered world. How far the cave goes down, or east, or west – nobody knows.

What they do know is that cave diving is dangerous, a high-risk game played only by those who have trained years to participate. Jill Heinerth, one of the world’s greatest cave explorers, has dived some of the planet’s most testing caves. We asked Jill to share with us five of her favourites:

Dan’s Cave, Abaco, Bahamas

It’s little surprise that one of the most aesthetically pleasing topside destinations on Earth also hosts some of the most beautiful underwater caves. Heinerth simply calls this the “prettiest cave on Earth.” Filled with incredible diversity, these ocean caves are literally filled with marine life such as sponges, lobsters, crabs and shrimp. The cave interior is so vulnerable that a single, reckless fin-kick can shatter mineral formations thousands of years old.

Source: Gary Schaut

Sally Ward Spring, Florida, USA

With diving prohibited only to research teams, many divers respect Sally Ward Spring cave as a particularly tricky dive. A tight entrance requires a hole needed to be dug out in order to fit through, but when you do and pass through the narrow corkscrew passage, the “most surprising room [appears] when you reach the balcony”. The little ledge is the entrance to a huge cube room, around 24 metres wide and 30 metres high. It’s like floating into an empty stadium, and even with a group of divers attempting to light the place with torches, most of the room remains dark.

Source: FastLaneDivers

Deep Blue Cave, Bermuda

Bermuda itself ranks high in the recent history of deep-sea exploration, and the destination now has a very active scientific diving community. Heinerth comments on its “stunning speleothems”, alien-like structures such as stalactites and stalagmites that divers have to carefully navigate through, along with “a beautiful entrance in Walsingham Preserve”, which is the first thing that divers get to see before embarking into the dark and narrow underworld.

Source: Ramon Llaneza Technical Diving

Sistema Dos Ojos, Quintana Roo, Mexico

This flooded cave system is close to Heinerth’s heart due to its endless beauty and because of her previous exploration efforts there. The name, which translates to “two eyes” in English, refers to two neighbouring cenotes which connect into a very large cavern zone shared between the two. One of the longest caves in the world, it is has been documented to stretch 61 kilometres, and offers divers the chance to surface into a bat cave.

Source: Absolute Adventure Mexico

The Shaft, near Mount Gambier, South Australia

Heinerth chooses this one for its uniqueness. It goes to show that underwater caves feature in the most unlikely of places: To access this cave divers have to enter through a tiny hole in the middle of a cow pasture. Even with incredibly powerful lights, the cave is so massive that there is often nowhere near enough light to illuminate it adequately. Upon descending into the sinkhole, the cave opens up into an incredible flooded theatre.

Source: Cave Diving Down Under