A pair of amateur explorers in Canada have found a vast underground passage stretching hundreds of metres underneath the bustling streets of Montreal whose formation dates back more than 15,000 years ago to the Earth’s last ice age.

“It’s just beautiful,” said Luc Le Blanc, who found the network of caverns earlier this year with fellow spelunker Daniel Caron. “The walls sometimes look like layers of fudge and chocolate; there’s brown, there’s dark brown, there’s ochre.”

The pair had for years poked around an existing cave in the city, known as the St Léonard cavern, suspecting that there was more to it. Discovered in 1812, the cave sits below a city park.

Facebook Twitter Pinterest The team drill into limestone to access the passage Photograph: Luc Le Blanc

In 2014, Caron – using dowsing, a technique sometimes used to locate ground water – detected an anomaly in the ground, suggesting a passage or a void could lie beyond the existing cave.

The following year they joined forces with another explorer to send a small camera through a fist-sized fissure at the end of the existing cave. While blurry, the images that came back suggested their hunch was correct.

Now all that was left was the gruelling task of piercing through the ancient limestone walls of the existing cave. The pair nearly gave up last year after their first attempt failed.

Facebook Twitter Pinterest The pair explore the underground cave. Photograph: Luc Le Blanc

They tried again in October and got lucky when a softer layer of the rock gave way, allowing them to drill and chisel a window through the limestone. “We could then see there was indeed a void and it was bigger than we thought,” said Le Blanc.



What they had found was an underground chamber about six metres in height, three metres wide and steeped in water. “It’s perfectly silent,” said Le Blanc. “The water is not moving. It’s not a river, it’s the water table.”

Formed thousands of years ago by massive glaciers that ruptured the rock beneath, yellow calcite line the walls of the passage at times, adding pops of bright colour while icicle-shaped stalactites hang overhead.

The pair crawled and waded through the passage, turning to inflatable canoes and swimming fins to help them navigate one passage where the water sat five-metres deep. “In that passage, its just beautiful. The walls are perfectly smooth, perfectly vertical and the ceiling is a perfectly horizontal slab,” said Le Blanc.

They were able to estimate that the passage way runs at least 250m before their travels were stymied by high water levels. “But it keeps going, so we have no idea where it will end,” said Le Blanc. “The ceiling and the floor are parallel but its sloping down. So as you go further and further into the cave, there’s more water and less air.” The hope is to return to the passage in early 2018 when the water levels recede.

On Monday, the city said it had commissioned a study of the cave in order to determine its exact depth and extent, with the hopes of one day opening the site to the public.

Some 350m north of recent find lies another cave, said Le Blanc. “We suspect these two caves are linked geologically and they might even connect, we don’t know yet.”

The many aspects that are still unknown about this recent find are thrilling, said Le Blanc, who has been exploring caves since 1977. “It’s a great discovery for us, we’re very happy about that,” he said. “In a caver’s lifetime, this doesn’t happen very often.”