Traveller to ancient city street spanning island (7)
I believe the answer is:
tourist
'traveller' is the definition.
(tourist is a kind of traveller)
'to ancient city street spanning island' is the wordplay.
'ancient city' becomes 'ur'.
'street' becomes 'st'.
'spanning' indicates putting letters inside.
'island' becomes 'i'.
'ur'+'st'='urst'
'urst' enclosing 'i' is 'urist'.
'to'+'urist'='TOURIST'
(Other definitions for tourist that I've seen before include "One travels for pleasure" , "Tripper, sightseer" , "Holiday visitor" , "Traveller for pleasure" , "Sightseeing traveller" .)