Bliss in getting back having sacked a great city (7)
I believe the answer is:
nineveh
'a great city' is the definition.
(ancient city)
'bliss in getting back having sacked' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nineveh that I've seen before include "Ancient city on the Tigris" , "old city" , "Ancient Assyrian city" , "Assyrian capital; Jonah preached against it" , "Ancient Assyrian capital" .)