Travel northwards through trees in French city (7)
I believe the answer is:
limoges
'french city' is the definition.
(I've seen this before)
'travel northwards through trees' is the wordplay.
'travel' becomes 'go' (synonyms).
'northwards' is a reversal indicator (in a down clue, letters go up or 'north').
'through' means one lot of letters goes inside another (inserted letters go through the word).
'trees' becomes 'limes' (lime is a kind of tree).
'go' written backwards gives 'og'.
'og' placed inside 'limes' is 'LIMOGES'.
'in' acts as a link.
(Other definitions for limoges that I've seen before include "French porcelain centre" , "French city noted for enamels and porcelain" , "French commune" , "foreign city" , "French city known for its porcelain" .)