Border with Italy shelters popular Adriatic resort (6)
I believe the answer is:
rimini
'adriatic resort' is the definition.
(I've seen this before)
'border with italy shelters popular' is the wordplay.
'border' becomes 'rim' (I've seen this before**).
'with' means one lot of letters go next to another.
'italy' becomes 'i'.
'shelters' indicates putting letters inside.
'popular' becomes 'in'.
'rim'+'i'='rimi'
'rimi' enclosing 'in' is 'RIMINI'.
(Other definitions for rimini that I've seen before include "Italian place" , "Italian coastal city" , "Italian holiday resort" , "N. Italian city" , "North-east Italian Adriatic resort" .)