Blue Grotto isle (5)
I believe the answer is:
capri
'blue grotto isle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for capri that I've seen before include "Neapolitan isle" , "Island near Naples" , "I carp about the island" , "Island in the Gulf of Naples" , "popular resort" .)