In the 50's and 60's the caves in the Mother Lode were frequent weekend goals.  Newcomers were taken first to the smaller, less decorated caves, but with the right attitude they would "work their way up" to  _ _ _ _ _ _ _ _ _ _ Cave.  (Even the names of the really superb caves weren't even uttered, except as code words, and then only behind closed doors.)

Then there was the old railroad tunnel in Oakland.  It had long soda straw stalactites and spectacular fungus growths eating away at the timbering.