What do you call a person who likes to explore caves?

A person who likes to explore caves is called a "caver" - if he or she is studying caves' scientific aspects, a "speleologist".

Caving is the amateur activity or sport of exploring caves. It was once known as 'spelunking' in the United States and Canada and 'potholing' (from the old Northern English term "pothole" for a cave whose entrance is a shaft open to the surface) in the United Kingdom and Ireland.

A person doing this activity is now generally a Caver: Spelunker and Potholer have fallen out of use though "Pothole" survives in a few Northern English caving-club names..

Speleology is the term for the study of caves, whether by amateur or professional scientists.