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.