Map mines the rich history of caves below city's homes

Hidden behind a tropical garden in the Auckland suburb of Mount Eden is a subterranean secret - a cave opening from the ground like the yawning mouth of a giant.

- EVA CORLETT

"People come down here and drop their jaws," said its owner, Sean Jacob, as he stood in the centre of the rock chamber. The cave is 106 metres long and up to five metres high. Part way in, the tunnel, which was formed when Mount Eden erupted 28,000 years ago, narrows and then opens into what Jacob calls "the ballroom" - a lofty area shimmering with golden minerals.

Beyond is a 10-metre crawl space that leads to another chamber. Jacob has attempted to enter it just once. "You draw blood," he said. "It is like going through a cheese-grater."

Aucklanders are familiar with the volcanic terrain of their city above ground, living side by side with 53 volcanoes. Yet many are unaware of the landscape concealed beneath their feet. Formed by volcanic eruptions, lava caves and tunnels are rare globally, and the sprawling patchwork beneath Auckland is unique to New Zealand. The city sits on top of roughly 200 known caves with a new cave being discovered every month, as construction increases and drilling tools become more sophisticated.