Where Anne Boleyn died, now modern flats (5,5)
I believe the answer is:
tower block
'modern flats' is the definition.
I don't understand the rest of the clue.
(Other definitions for tower block that I've seen before include "big build-up?" , "Tall residential or office building" , "at which 29 [BOLEYN] finished?" , "Skyscraper" , "large building" .)