There are so many sites in this category but the most iconic (besides the politics) is Hashima Island. Cranes, dry docks, and even Glover House is historical but nothing compares to Battleship Island. It's a small island about one hour boat ride out of Nagasaki. The island had over 5000 inhabitants who dug coal deep into the undersea. It was a self sustaining island with hospitals, theatre, markets etc

Since it was abandoned decades ago, the typhoons have devastated the buildings and today it looks really scary like a crumbling deserted ghost town on an island with fortress like sea walls. A Chernobyl but vastly poorer condition.

There are several boats that take tourist to visit the island and these boats take their turn landing. You get 45 mins on land and there are developed walking areas to only a small portion of the island. Book early as this has become very popular with locals since WHS. I tried 6 months early and nearly did not get on. There are several on line sites to book. The tours are all in Japanese and so I hired a guide to translate for me.

Also try to go in spring or fall when the weather is good. I was told that in August, only half the trips could land due to high swells. If they do not land then they refund you 300 yen of the fare. Even on a good day several passengers were sick.

The site has the irony of industry decaying.