My gold boxes free in passage (8)
I believe the answer is:
corridor
'passage' is the definition.
(corridor is a kind of passage)
'my gold boxes free' is the wordplay.
'my' becomes 'cor' (I've seen this in other clues).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'boxes' is an insertion indicator (the outside letters must 'box' inside letters in).
'free' becomes 'rid' ('rid' can be a synonym of 'free'**).
'cor'+'or'='coror'
'coror' placed around 'rid' is 'CORRIDOR'.
'in' is the link.
(Other definitions for corridor that I've seen before include "Train's aisle" , "Long passageway" , "Passage connecting rooms" , "way through" , "Indoor passageway" .)