Organised hen do in smart European port (9)
I believe the answer is:
trondheim
'european port' is the definition.
(Trondheim is a port in Norway)
'organised hen do in smart' is the wordplay.
'organised' indicates an anagram.
'in' means one lot of letters goes inside another.
'smart' becomes 'trim' (synonyms).
'hen'+'do'='hendo'
'hendo' is an anagram of 'ondhe'.
'ondhe' placed into 'trim' is 'TRONDHEIM'.
(Other definitions for trondheim that I've seen before include "'Nidaros'" , "Norwegian city" .)