The most common and most likely answer to this crossword clue is the 6 letter word OPORTO
I've seen this crossword clue in The Guardian
O
P
O
R
T
O
More clues leading to the result OPORTO
- Two ducks crossing harbour in European city
- Poor travelling to Portuguese city
- Ducks seen outside harbour town and city
- Left during no-score draw for City
- Nothing ordinary’s left inside European city
- Whence fortified wine once produced? On river there only, originally
- Portuguese location in which there’s nothing left – nothing!
- European city left in good heart
- Poor to riot in Portuguese city
- Content to shop or tour city
Buddy explains!
The straight part
We know that "Whence fortified wine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case whence fortified wine = oporto.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.