What are explored caves called?

Answer 1

Cavers, as simple as that, whether visiting well-known caves or exploring ones they have just discovered (that can be a wonderful experience!).

The science of caves and their natural contents is called Speleology but many speleologists still call themselves cavers.

I looked into the old word "spelunker" you see quoted on Answers occasionally. It seems it was coined from a Greco-Latin mix by American cavers in the 1940s, but not used in other countries. Though originally perfectly innocent, in the 1960s it started to become a derogatory term used by cavers themselves for ill-equipped, rather inept novices.

Answer 2

Spelunkers (amateur or sportive) and speleologists for the more scientific types, its like Fish Fanciers, and Icthyologists, one much more technically involved. +++

The word "spelunker" is rarely used by cavers, certainly not outside of the USA anyway - all the English-language texts I've seen use the second word: "caver".

Subsequently to posting the above edit, I looked into the word "spelunker". It was invented by a group of American cavers and used without fear or favour in the US, though not elsewhere, for a couple of decades or so. Then it started to become a sarcastic term for novices and, more especially perhaps, ill-equipped dilettantes, which explains its disappearance from mainstream caving literature.