Stumbled across your adventures whilst researching for my upcoming holiday to Japan.
I’ve always found this sort of thing intensely interesting but unfortunately there’s not a whole lot to explore here in Australia. Places aren’t generally left in abandonment for too long and are usually hastily redeveloped.

Anyway, after reading your wish-list of places to explore and noticing you mentioned a nuclear bunker.

Well, it may not be abandoned, nor really something you can explore on your own (as far as i know anyway) but there are a few of these around Prague. I toured one just last year after stumbling across a guide in the main square of Prague itself. You can identify these guys by their brightly coloured umbrellas.
It was a cheap, fun and fascinating tour.

If ever you’re in that part of the world if may be an opportunity to check another off your list!

Velo

ps: One thing you might add to your list is Wajima, a fishing village on the Noto Honto. A bit out of the way, but a very interesting piece of what some people refer to as “real” Japan. I don’t know about actual Hiakyo, but in a sense the whole village is a kind of Hiakyo, as the fishing industry is in rapid decline, and the literally thousands of mostly docked boats and other fishing related paraphernalia are exceedingly interesting and photogenic.