Jeju is a volcanic island off the southern coast of South Korea, dominated by Mount Hallasan and a landscape of forested uplands and volcanic cones. In the final months of the Pacific War, the Japanese military transformed this remote island into a heavily fortified defensive base, excavating tunnels, command posts, shelters, and artillery positions throughout its interior.

Many of these underground positions were dug into the slopes of Hallasan and the surrounding volcanic terrain, often with the forced labor of local residents. Entrances were concealed among forests and hillsides, while networks of chambers and passageways prepared the island for an Allied invasion that never came.

Decades later, the tunnels remain scattered beneath an apparently peaceful landscape—some collapsed, others overgrown or hidden from view. Jeju appears whole above ground, yet beneath its surface survives an architecture of fear and preparation, hollowed into the earth and abandoned when the war ended.