Good of French to bring wine inside stronghold (7)
I believe the answer is:
bastion
'stronghold' is the definition.
(bastion is a kind of stronghold)
'good of french to bring wine inside' is the wordplay.
'good of french' becomes 'bon' ('good' in French).
'to bring wine' becomes 'asti' (I can't explain this - if you can you should give a lot more credence to this answer).
'inside' indicates putting letters inside.
'bon' going around 'asti' is 'BASTION'.
Can you help me to learn more?
(Other definitions for bastion that I've seen before include "fortress" , "Stronghold, fortification" , "Defence - in boats (anag)" , "'Stronghold, citadel (7)'" , "that's fortified" .)