Reserve this place in Nice on protruding coastline (7)
I believe the answer is:
iciness
'reserve' is the definition.
(I've seen this in another clue)
'this place in nice on protruding coastline' is the wordplay.
'this place in nice' becomes 'ici' ('here' in French).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'protruding coastline' becomes 'ness' (ness can mean a headland or promontory).
'ici'+'ness'='ICINESS'
(Other definitions for iciness that I've seen before include "Hostility, unfriendliness" , "Extreme cold" , "Unapproachability" , "Chill; reserve" , "Extreme hostility" .)