Trip to ancient city (4)
I believe the answer is:
tour
'trip' is the definition.
(a journey or expedition)
'to ancient city' is the wordplay.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'to'+'ur'='TOUR'
(Other definitions for tour that I've seen before include "Travel around" , "Trip, visit" , "Rout on excursion" , "Term of duty" , "A trip round" .)