Looking back in some secret rooms (5)

I believe the answer is:

retro

'looking back' is the definition.
(I've seen this before)

'in some secret rooms' is the wordplay.
'in' indicates a hidden word.
'RETRO' can be found hidden inside 'some secret rooms'.

(Other definitions for retro that I've seen before include "Backward looking" , "Style derived from the past" , "Looking backwards" , "Prefix for old-style" , "Imitative of an older style" .)

I've seen this clue in The Telegraph.

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