In 2015, secret tunnels and underground facilities were discovered near the site of the former Hitoyoshi Naval Air Base, built during World War II.

In preparation for an American invasion, the Japanese Navy constructed facilities underground in this mountainous region. They included areas for manufacturing torpedoes, as well as command-and-control bunkers to prepare the defense of the mainland. Additionally, a section of the base area was dedicated to the manufacture of aviation fuel using the roots of local pine trees.

After these underground facilities were discovered, a museum was later opened in 2018. It includes above-ground exhibitions, as well.