spe·lunk·er 
(spĭ-lŭngkər, spēlŭng′-)
(spĭ-lŭngkər, spēlŭng′-)n.
One who explores caves chiefly as a hobby; a caver.
[From obsolete spelunk, cave, from Middle English, from Old French spelunque, from Latin spēlunca, from Greek spēlunx.]
spelunk′ing n.