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.