Matsushiro Underground Imperial Headquarters

The Matsushiro Underground Imperial Headquarters is a vast complex of tunnels excavated in the closing phase of the Second World War at Matsushiro, now part of Nagano City. The tunnels run beneath three mountains — Zozan, Maizuruyama and Minakamiyama — and total about 10 kilometres. The military intended the site as a last-resort refuge to which the Imperial General Headquarters, the Emperor and the Imperial Palace, and the central organs of government would move for the expected "decisive battle" on the home islands. Zozan was planned for government agencies and the national broadcaster, Maizuruyama for the headquarters and the imperial residence, and Minakamiyama for storage.

Work began in extreme secrecy with a blast at 11:11 a.m. on 11 November 1944 and continued for about nine months; roughly 75 percent of the plan had been completed when Japan surrendered in August 1945. At the peak in April 1945 about 10,000 people were working on the site, around 7,000 Koreans and 3,000 Japanese, supplemented by conscripted labourers and students, for a cumulative total of several hundred thousand worker-days. Many of the Korean workers had been forcibly mobilized and laboured at dangerous underground work in harsh conditions. No complete record of deaths survives. One estimate holds that about 1,500 Koreans died, but the true figure is unknown and accounts differ; the explanatory sign installed by Nagano City likewise records differing views on how far the mobilization was compulsory.

After the war the Maizuruyama facilities were taken over, from 1947, by the Japan Meteorological Agency's Matsushiro Seismological Observatory. The Zozan tunnels are managed by Nagano City, which has opened about 500 metres from the western entrance to visitors since around 1989–1990. A memorial to the Korean victims was erected near the entrance in 1995.

Near the Zozan entrance the privately run museum Mo Hitotsu no Rekishikan Matsushiro ("Another History Museum") documents the forced labour and the construction. Inside the tunnels, drill marks and the impressions of trolley sleepers are still visible. The site conveys both the final plans of the wartime state and the experience of the workers who built it.