Gunhamdo

A Japanese island, 9 miles from Nagasaki, enlarged & used from 1897 to 1974 to mine coal w/shafts going down 2/3 of a mile beneath the sea. Oddly, given the Pacific rim geologic history of subduction, that there's massive sedimentary (typically surface heavily vegetated wetlands) deposits of coal forming there. It's common name is Gunkanjima, meaning battle ship. The actual name is Hashima Island. From the '30s to the end of WWII Chinese & Korean conscripts/prisoners numbering in the thousands worked those mine shafts w/80+ temps & 95% humidity & some might say brutal treatment. During that time period an estimated 1300 miners died.

The movie mixes factual & fictionalized events. Kudos goes to the production of one of the best movie sets/props I've ever seen (actually built in Chuncheon, Korea) - Game of Thrones level. Also to the costuming & makeup personnel for the grimy authenticity & cinematography for the great camera work. Acting was spot-on although as is typical in these types of films the baddies (the Japanese in this case) are made to be really bad dudes. Forewarned - lots of violence, especially towards the end.