Re tunnels:  Check out a  mid 30s Columbia film where Victor Jory

          plays a tunnel engineer, and  a  Fred MacMurray-Claudette Colbert

          Paramount romantic comedy, probably by Mitchell Leisen, where she

          is  a reporter and he is  a "sandhog". You can get the titles and

          many other citations in  the  AFI catalogs. Also,  of course, The

          Great Escape. For  sf, Unknown World  (1951) begins  by tunneling

          with some kind of device through a volcano (repeated in  the 1993

          version of Journey to  the Center  of  the Earth), before turning

          into a loose adaptation of  the Verne novel, which features caves

          and  caverns.  Also   ER  Burroughs's  At   the   Earth's   Core.