Theatre is turned into great unopened shopping centre (5,4)
I believe the answer is:
music hall
'theatre' is the definition.
(music hall is a kind of theatre)
'is turned into great unopened shopping centre' is the wordplay.
'turned' indicates anagramming the letters.
'into' is an insertion indicator.
'great' becomes 'much' (I can't explain this - if you can you should give a lot more credence to this answer).
'unopened' means to remove the first letter (the opening of the word is removed).
'shopping centre' becomes 'mall' (a mall is a large shopping complex).
'is' anagrammed gives 'si'.
'si' placed inside 'much' is 'musich'.
'mall' with its initial letter taken off is 'all'.
'musich'+'all'='MUSIC-HALL'
Can you help me to learn more?
(Other definitions for music hall that I've seen before include "Vaudeville" , "Late 19th century entertainment, and the theatre it took place in" , "Form of variety" , "theatre of a sort" , "Mainly C 19 variety entertainment" .)