That woman in ancient city is a guide (5)
I believe the answer is:
usher
'a guide' is the definition.
('usher' can be a synonym of 'guide')
'that woman in ancient city' is the wordplay.
'that woman' becomes 'she' (I've seen this before).
'in' indicates putting letters inside.
'ancient city' becomes 'ur'.
'she' inserted into 'ur' is 'USHER'.
'is' acts as a link.
(Other definitions for usher that I've seen before include "One puts you in your place" , "Doorkeeper, escort" , "Old teacher" , "whose house collapsed?" , "Person whose job is to conduct others" .)