A caver is someone who goes into underground caves as a sport.
caver in American English
(ˈkeivər)
noun
a person who studies or explores caves
Word origin
[1645–55; cave + -er1]This word is first recorded in the period 1645–55. Other words that entered Englishat around the same time include: capsule, cruise, elastic, halftone, regulator-er is a suffix used in forming nouns designating persons from the object of their occupationor labor (hatter; tiler; tinner; moonshiner), or from their place of origin or abode (Icelander; southerner; villager), or designating either persons or things from some special characteristic or circumstance(six-footer; three-master; teetotaler; fiver; tenner)