Iberian city ducks circle harbour (6)
I believe the answer is:
oporto
'iberian city' is the definition.
(I've seen this before)
'ducks circle harbour' is the wordplay.
I cannot quite understand how this works, but
'circle' could be 'o' (O is a circle) and 'o' is found within the answer.
'harbour' could be 'port' (I've seen this before) and 'port' is located in the answer.
A single letter 'o' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for oporto that I've seen before include "European city" , "Portuguese wine city" , "Second largest city in Portugal" , "Portugal's second city" , "Wine city in Portugal" .)