Narrow promontory around large city in the Balkans (5)
I believe the answer is:
split
'city in the balkans' is the definition.
'split' can be an answer for 'city' (I have seen 'European city' mean 'split' so perhaps 'city' could also mean 'split'). I am unsure of the 'in the balkans' bit.
'narrow promontory around large' is the wordplay.
'narrow promontory' becomes 'spit' (I can't explain this - if you can you should believe this answer much more).
'around' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'spit' going around 'l' is 'SPLIT'.
Can you help me to learn more?
(Other definitions for split that I've seen before include "Break; leave suddenly" , "Break in pieces - leave" , "Break forcibly" , "European city" , "Crack; divide" .)