Archaeologists from the Japanese Archaeological Associated were permitted to enter the Gosashi Tomb complex in February. They have published the results of the visit.
The Gosashi Tomb complex is the burial place for members of the Japanese Imperial Family, and dates back to the Fifth Century.
From the article:
"The event marked the first time that scholars had been allowed inside a royal tomb outside of an official excavation led by Japan's Imperial Household Agency.
Archaeologists have been requesting access to Gosashi tomb and other imperial sites since 1976, in part because the tombs date to the founding of a central Japanese state under imperial rule.
But the agency has kept access to the tombs restricted, prompting rumors that officials fear excavation would reveal bloodline links between the "pure" imperial family and Korea—or that some tombs hold no royal remains at all.
Although the team's visit didn't lay any of those issues to rest, experts celebrated it as a first step toward expanded access to the mysterious tombs."
Apparently, the Gosashi Tomb is also the resting place for the legendary Empress Jingu, who acted as regent for her son in 200AD.