I've already visited the one restored castle in Okinawa and Wikipedia tells me there are several other ruined castles here on the main island.
But one castle is mentioned several times yet I cannot find its whereabouts, it is called Yamada Castle.
Wikipedia does not give latitude and longitude, Wikivoyage doesn't mention it, Google Maps doesn't find it. I've also tried OpenStreetMap and the official site of the nearest town or village in Japan, all to no avail.
It is mentioned that Zakimi Castle was build using materials from Yamada Castle, yet it is mentioned in several places that some ruins remain, so not everything was taken. In any case I'm interested in the location and surroundings even if there's not a lot to see.
As I'm thinking of hitchhiking north with my tent I'd be keen to find it as it's now the most mysterious one for me.