Wandering cavers see endlessly deep crack (8)
I believe the answer is:
crevasse
'crack' is the definition.
(crevasse is a kind of crack)
'wandering cavers see endlessly deep' is the wordplay.
'wandering' indicates anagramming the letters.
'see endlessly' means to remove the last letter.
'deep' becomes 'sea' (I've seen this before).
'sea' with its final letter taken off is 'se'.
'cavers' with letters rearranged gives 'crevas'.
'crevas'+'se'='CREVASSE'
(Other definitions for crevasse that I've seen before include "Sever sac (anag)" , "big split" , "Crack in a mountain slope or a glacier" , "climbing hazard in glacier" , "Deep fissure in a glacier" .)