French city maintains empty room for opera (6)
I believe the answer is:
'opera' is the definition.
(I've seen this before)
'french city maintains empty room' is the wordplay.
'french city' becomes 'caen' (I've seen this in another clue).
'maintains' is an insertion indicator.
'empty' says to hollow out the word (remove centre letters).
'room' with its middle taken out is 'rm'.
'caen' going around 'rm' is 'CARMEN'.
'for' acts as a link.
(Other definitions for carmen that I've seen before include "Spanish opera by Bizet" , "Bizet's great Spanish opera" , "Musical from Bizet opera" .)