Sydney’s secret underwater tunnels revealed

Niamh Hannon

They are not like anything you have ever seen before and experts are baffled about why these secret underwater tunnels have been built.

Located beneath the ancient sandstone of Georges Head is a network of tunnels concealed on the sea floor, easily accessible to divers.

A manmade tunnel which leads down to a hidden staircase and cavern has been revealed.

Only divers can access the network of tunnels. Image: 7news
Only divers can access the network of tunnels. Image: 7news

Historians believe this could date back to the 1870s, when explosives were laid in the harbour to guard against an enemy invasion.

Historians believed they could date back to the seventies. Image: 7news
Historians believed they could date back to the seventies. Image: 7news

Historian Peter Hobbins said: "As an enemy ship goes past, you push the button, connect the wires, and potentially blow it up. You create what you would call a killing zone these days."

However experts are still trying to work out what the tunnel was used for.

There are lots of theories about what the tunnels were used for. Image: 7news
There are lots of theories about what the tunnels were used for. Image: 7news

During WWII, an anti-submarine boom net was built between Georges Head and Green Point. Historians say this could have been where it connected to land.

There are other theories. A tall shaft at the end could have been for ventilation, or for a quick getaway.

The tunnels are under Sydney harbour. Image: 7news
The tunnels are under Sydney harbour. Image: 7news
It is unknown what they were used for. Image: 7news
It is unknown what they were used for. Image: 7news

This extraordinary piece of history is just a 15 minute boat trip from Mosman in Sydney.