Touring French Riviera town, he heightens the quality (8)
I believe the answer is:
enhances
'heightens the quality' is the definition.
'enhances' can be an answer for 'heightens' ('enhance' can be a synonym of 'heighten'). I am unsure of the 'the quality' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for enhances that I've seen before include "Adds to" , "Heightens, intensifies or increases in value" , "Makes better or heightens" , "Improves or increases intensity" , "Increases attractiveness or other qualities of" .)