The gigantic keyhole tombs in Japan

I've never spent much time around Osaka prefecture - is that why I hadn't actually heard of the gigantic "keyhole" tombs near it, which are explained in this BBC video?  Here's a photo:

Pretty interesting - and pretty amazing how Japan doesn't believe in any form of archaeological digging on them.  

All good stuff for a science fiction/fantasy movie, too, I would imagine.  Probably already been done in some anime already, I suspect.