On a sunny autumn morning, a group of about 10 families, looking no different from ordinary hikers, gathers at JR Takao Station. The station usually serves as a gateway to Mount Takao and other well-known trekking areas west of Tokyo. But this group’s destination is strikingly different.

Walking along a gorge between Mount Konpira and Mount Hatsusawa, which lie in front of Mount Takao, the chatting group soaks up the fragrant forest air. The cheerful mood, however, suddenly changes as they arrive at the mouth of a dark tunnel.

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