The hills around Rabaul are riddled with Japanese military tunnels from the Second World War — an underground system built under constant Allied bombing that effectively put the entire military apparatus underground. Several of these tunnels are open to visitors and provide an extraordinary and somewhat eerie window into the experience of Japanese forces during the Pacific War.
The most visited section is the tunnel complex near the town centre, where a series of chambers were used as a command headquarters and later as storage for ammunition and supplies. The tunnels retain original metal tracks, ventilation equipment, and various artefacts left by the Japanese forces. A local guide (usually arranged through guesthouses) will explain the tunnel function and history and is genuinely worth having — the system is extensive and disorienting without guidance. The site is sobering: the Japanese forces who built these tunnels never left Rabaul, surrendering or dying here at the end of the war.