The most common and most likely answer to this crossword clue is the 9 letter word LENINGRAD
L
E
N
I
N
G
R
A
D
More clues leading to the result LENINGRAD
- Lake in garden transformed foreign city once
- Liberal revelling in danger in Soviet city
- Take some glen in, gradually finding old city
- European in bustling Darlington withdrawing to old city
- Student revelling in danger in Saint Petersburg
- Sloping road with one moving forward to reach old city
- … needed again with heater fitted in Soviet city
- Ruined garden left in Soviet Union city
- Name favoured by Greek in principal Soviet city
- Soviet city‘s tendency to dismiss a radical
Buddy explains!

The straight part
We know that "old city" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old city = leningrad.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.