The most common and most likely answer to this crossword clue is the 9 letter word CATACOMBS
I've seen this crossword clue in The Times
C
A
T
A
C
O
M
B
S
More clues leading to the result CATACOMBS
- Animals having a search inside underground tunnels
- Chaps going about a search for excavated burial-places
- Kitty, heading for Altamira, scours series of caves
- Places for burying 15s around a fellow doctor
- Musical involving a search for burial places
- Mexican dish in county for ancient burials
- Jazz fans holding a thorough search for dark passages
- ABC mascot defaced burial sites
Buddy explains!

The straight part
We know that "caves" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case caves = catacombs.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CATACOMBS mean?
CATACOMBS noun- (often plural) An underground system of tunnels and chambers with recesses for graves, used (in former times) as a cemetery; a tunnel system used for burying the dead, as in Paris or Ancient Rome.