Animals having a search inside underground tunnels (9)
I believe the answer is:
catacombs
'underground tunnels' is the definition.
'animals having a search' is the wordplay.
'animals' becomes 'cats' (I've seen this before).
'having' is an insertion indicator.
'search' becomes 'comb' (combing is a kind of searching).
'a'+'comb'='acomb'
'cats' placed around 'acomb' is 'CATACOMBS'.
'inside' acts as a link.
(Other definitions for catacombs that I've seen before include "burial place" , "Underground burial chambers" , "Underground cemeteries constructed by the ancient Romans" , "Vaults" , "Underground burial places" .)