Trip to an ancient city (4)
I believe the answer is:
tour
'trip' is the definition.
(a journey or expedition)
'to an ancient city' is the wordplay.
'an ancient city' becomes 'ur' (ancient Sumerian city state).
'to'+'ur'='TOUR'
(Other definitions for tour that I've seen before include "Journey to visit places of interest" , "Extensive journey" , "Short trip; spell of duty" , "Journey around" , "Journey visiting several different places" .)