On a scorching hot day in late June, some 20 tourists were gazing at the fenced-off entrance of an abandoned tunnel named Taura Zuido (Taura Tunnel) in the Kanagawa Prefecture port city of Yokosuka.

Yoshiyuki Hiranuma, who was guiding that "Old Tunnels of Yokosuka" tour, explained that the Taura Zuido tunnel is 80 meters long and was constructed by local volunteers in 1893 as a shortcut for workers at a munitions factory.

"It was used until 1923, when a new and bigger tunnel was made," Hiranuma, an authority on abandoned roads and tunnels, told the group.