Cool Paris trashed Athenian citadel (9)
I believe the answer is:
acropolis
'athenian citadel' is the definition.
'acropolis' can be an answer for 'citadel' (acropolis is a kind of citadel). I am unsure of the 'athenian' bit.
'cool paris trashed' is the wordplay.
'trashed' is an anagram indicator.
'cool'+'paris'='coolparis'
'coolparis' anagrammed gives 'ACROPOLIS'.
Can you help me to learn more?
(Other definitions for acropolis that I've seen before include "Athens landmark" , "Upper fortified part of Greek city - Athens's is famous" , "high point" , "Upper fortified part of Greek city as in Athens" , "classical site" .)