Walking the streets of Montreal, Canada, you’d probably never guess a cave system lurked 10 meters below. But that’s exactly what two speleologists, or cave experts, recently discovered. Daniel Caron and Luc Le Blanc found a 15,000-year-old network of caverns that might have formed as glaciers receded during Earth’s last Ice Age. They think it’s possible that no person had ever set foot inside these caves until now.

Back in 1812, the Saint Léonard cave beneath Pie-XII Park was discovered. But cave experts wondered if there was more. Caron and Le Blanc, both amateur explorers, found a vast network in October after drilling through the limestone walls of the existing cave to expose a spacious chamber which branches off into several passages winding beneath the Saint-Leonard borough.
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The cave system could have formed as pressure from colossal glaciers split the rock. The explorers uncovered between 250 and 500 meters (820 to 1,640 feet) of caves, according to The Canadian Press, although they think the actual dimensions are even longer. The furthest reaches extend to the Montreal water table, Caron said.
Rock climbing equipment is necessary to explore some passages, and some may need more rock-breaking for a team to go inside. The team was stopped by water and could only partially explore one of the passages via an inflatable raft, but they aim to explore more in the dry season when the water level hopefully lowers.
As the explorers only reached the system by drilling, they think it’s likely no other human beings have ever walked inside these caves. Caron said every caver’s dream is to find a place no one’s been before. He told The Canadian Press, “Normally you have to go to the moon to find that kind of thing.”