While touring at that time one sees old city (6)
I believe the answer is:
athens
'old city' is the definition.
(ancient city)
'while touring at that time' is the wordplay.
'while' becomes 'as'.
'touring' means one lot of letters goes inside another (touring can mean going round).
'at that time' becomes 'then' (synonyms).
'as' going around 'then' is 'ATHENS'.
'one sees' is the link.
(Other definitions for athens that I've seen before include "Tan she got in Greece" , "Hasten to European city" , "Hen sat down in the city" , "6 capital" , "Mediterranean capital" .)