Long to be right inside grotto (5)
I believe the answer is:
crave
'long' is the definition.
(thesaurus)
'right inside grotto' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' indicates putting letters inside.
'grotto' becomes 'cave' (I've seen this before).
'r' inserted inside 'cave' is 'CRAVE'.
'to be' acts as a link.
(Other definitions for crave that I've seen before include "need, desperately" , "Beg; long for" , "Hunger for" , "Feel a powerful desire for (something)" , "Powerfully desire" .)