Explorers in Montreal have made the underground discovery of a lifetime: a giant cave that weaves under one of the city’s public parks.

A cave below Parc Pie-XII in Saint-Leonard, a neighbourhood in Montreal, was already available for people to walk through. But Luc Le Blanc, one of the people credited with the most recent discovery, says the new section was uncovered just behind the old cave.

The newly-discovered cavern is 10 times bigger than the existing caves and dates back 15,000 years, according to experts in the field.

“It's a dream,” Le Blanc told CTV Montreal. “It only happens to you a couple of times in a lifetime and less frequent here in northern latitudes.”

While most caves are formed through water erosion, these ones are glaciotectonic, meaning they formed through glacial pressure during the Ice Age.

To find the caves, Le Blanc and his colleague used dowsing in the area, a technique typically used to find water, where they discovered a void beyond the known cave. A year later, they came back and with camera to see what lay beyond the cave walls.

Getting to the new area proved a bigger challenge as it required digging through limestone. The crew had all but given up, but in October they caught a break with some softer rock and were able to make a hole.

Eventually, the pair had a tunnel big enough to squeeze through and were able to explore the other side. They traversed the newfound cave on foot at first and then, when they reached water, using an inflatable boat.

High water levels have stopped the explorers from checking out the full size of the cave, but once the water recedes, they plan to see what other discoveries they can make.

It remains to be seen if this new section will be open to the public, but at least one city councillor is optimistic about the cave’s potential tourist impact.

“Normally people that go and visit a cavern it's far away and so on,” said Dominic Perri, councillor for Saint-Leonard West. “This is in an urban setting, so I think there's a big potential.”

With a report from CTV Montreal’s Denise Roberts