日吉台地下壕, Naval underground bunker in Kohoku Ward, Yokohama, Japan
Hiyoshi is an underground bunker built with concrete tunnels that runs beneath Keio University campus and contains connected passageways. Multiple chambers housed command centers, radio stations, and power generators that allowed operations to be directed from below ground.
The Navy built this facility in 1944 after the previous fleet headquarters was destroyed in combat. From this new location, naval operations were supposed to be directed until the facility was abandoned after the war ended.
The site is called Hiyoshi and was built by the Navy to direct strategic operations from underground. Visitors can walk through the preserved rooms today and see how people worked in these spaces during wartime.
The entrance descends a steep slope and then continues horizontally through passages with ventilation shafts and pipes along the walls. Visitors should expect uneven floors and low ceilings, so sturdy shoes and a flashlight are helpful.
An unexpected feature is the installation of fluorescent lighting, which was uncommon in civilian structures of that period and shows how sophisticated the underground facility was equipped. This lighting allowed workers to remain focused even without daylight.
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