Cave not entirely unpleasant? Nothing more (6)
I believe the answer is:
grotto
'cave' is the definition.
(I've seen this before)
'not entirely unpleasant? nothing more' is the wordplay.
'not entirely' means to remove the last letter.
'unpleasant?' becomes 'grotty' ('grotty' can be a synonym of 'unpleasant').
'nothing more' becomes 'o' (resembles 0).
'grotty' with its final letter taken off is 'grott'.
'grott'+'o'='GROTTO'
(Other definitions for grotto that I've seen before include "(Imitation) cave" , "Artificially or naturally ornamented cave" , "A picturesque cave as in Lourdes (6)" , "Type of cave, often with religious significance" , "Fancy cave" .)