I remember, in one of my readings, that was in Wikipedia, something about the Matsushiro Underground Imperial Headquarters, Coordinates: 36.545811°N 138.203931°E
The Matsushiro Underground Imperial Headquarters (松代大本営跡 Matsushiro Daihon'ei Ato?, was a large underground bunker complex built during the Second World War in the Matsushiro suburb of Nagano, Japan.
The facility was constructed so that the central organs of government of Imperial Japan could be transferred there. In its construction, three mountains, symbolic of Matsushiro Municipality were damaged.
Parts of the caves are open to the public today, and are operated as a tourist attraction by Nagano.
Construction
Construction began on November 11, 1944 and continued until Japan's surrender on August 15, 1945. Construction was 75% completed at the end of the war, with 5,856.6 square meters (63,040 sq ft) of floor-space (59,635 cubic meters (2,106,000 cu ft) of volume) excavated.
Between 7,000 and 10,000 Korean slave laborers were used to build the complex, and it is estimated that 1,500 of them died. Forty-six Koreans disappeared on August 15, 1945, when Japan surrendered. The project cost ¥200,000,000
A diagram of the complex
The complex was an interlinked series of tunnels underneath several mountains. Facilities for theImperial General Headquarters and palace functions were constructed under Mount Maizuru; military communications under Mount Saijo; government agencies, NHK and central telephone facilities under Mount Zōzan; the residences of the imperial family under Mount Minakami, and the Imperial Sanctuary under Mount Kobo.
The original purpose of the complex was to serve as an alternative headquarters for the Imperial General headquarters. However, in March 1945, secret orders were issued to add a palace to the complex. Yoshijirō Umezu informed Emperor Hirohito about construction of the complex in May, but did not tell him that it contained a palace.
This is a lengthy description in Wikipedia and to avoid distracting our thread i will post most of the description on the thread "Why Tunnels Are Round".
But what struck me most is this lines
While the project was an operational secret in the guise of a warehouse, from the statement of a local Japanese labourer, rumours were rife in the surrounding villages and towns that the emperor was coming to town. The cause of the rumours was due to the massive amounts of cargo that came on trains.
see below attachment of the Diagram for the said Imperial Japanese Tunnel Complex.
I believe, this is the fortress of them all, above all other wartime Imperial Japanese Tunnel Complexes----THE SUPPOSED RESTING PLACE OF ALL LOOTED TREASURES.
Gboy, does the one you're holding looks like this?