Some tunnels for invisible island expansion in the South China Sea?

 https://www.scmp.com/news/china/science/article/3263487/scientists-propose-tunnels-invisible-island-expansion-south-china-sea?module=top_story&pgtype=homepage

Its an old and a new thing, depending upon where one looks.

https://timesofindia.indiatimes.com/travel/travel-news/china-4300-year-old-secret-tactical-defence-tunnels-unearthed/articleshow/106543780.cms

https://www.washingtontimes.com/news/2023/oct/25/inside-ring-new-details-chinas-underground-nuclear/

https://nypost.com/2020/08/05/inside-chinas-underground-doomsday-city-dubbed-the-dungeon/

https://thedigitallabyrinth.blogspot.com/search?q=tunnels