From the website "Subterranea Britannica is a UK-based society for all those interested in man-made and man-used underground structures and space. Founded in 1974, the society (often known simply as Sub Brit) has grown to over a thousand members. Our interests cover all manner of underground sites, from Neolithic flint mines to nuclear bunkers. Many of these sites are documented on this website. Some can be easily visited, others require more specialist training or equipment; some, sadly, no longer exist."