Good French wine is kept in stronghold (7)
I believe the answer is:
bastion
'stronghold' is the definition.
(bastion is a kind of stronghold)
'good french wine is kept' is the wordplay.
'good french' becomes 'bon' ('good' in French).
'wine' becomes 'asti' (Italian wine).
'is kept' is an insertion indicator.
'bon' enclosing 'asti' is 'BASTION'.
'in' acts as a link.
(Other definitions for bastion that I've seen before include "Strong defender" , "part of stronghold" , "Obtains (anag.)" , "that's fortified" , "Obtains in fortified place or stronghold" .)