City is huge, look! (4)
I believe the answer is:
oslo
'city' is the definition.
(capital of Norway)
'huge look' is the wordplay.
'huge' becomes 'os' (abbreviation for outsize).
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'os'+'lo'='OSLO'
'is' acts as a link.
(Other definitions for oslo that I've seen before include "Norwegian city, formerly Kristiania" , "Norwegian chief port" , "European capital in go-slow" , "Norwegian capital" , "foreign port" .)