All u ever wanted to know about the Underground

Came across a very interesting website called Subterranea Britannica

Formed in 1974, Subterranea Britannica is a society devoted the the study and investigation of man-made and man-used underground places. Cold War related material is covered separately here: COLD WAR -Bunkers etc. Subterranea Britannica brings together people with an interest in all types of underground space – from deneholes to dug-outs and from souterrains to subways – see the sites pages. Indeed, as the list shows, there are at least seventy categories of underground excavations that are of particular interest to our members