Garden Island Tunnel System

The Garden Island Tunnel System, also known as Garden Island tunnels, Garden Island Tunnel Complex and Potts Point Tunnels, is a former tunnel warfare system in Garden Island, Sydney, Australia. Used in World War II by the Royal Australian Navy in 1941, the tunnels were dug from sandstone beneath Potts Point after the Japanese attacked Pearl Harbor, to shelter the men working at the naval base from air raids.

Source: Wikipedia — Garden Island Tunnel System (CC BY-SA 4.0)