Walk where mountains crossed by East European to the west (9)
I believe the answer is:
esplanade
'walk' is the definition.
(esplanade is a kind of walk)
'mountains crossed by east european to the west' is the wordplay.
'mountains' becomes 'alps' (European mountain range).
'crossed by' indicates putting letters inside (inserted letters are crossed or covered by others).
'east' becomes 'e' (synonyms).
'european' becomes 'Dane' (someone from Denmark).
'to the west' says the letters should be written in reverse (letters written right to left or 'east to west').
'e'+'dane'='edane'
'alps' going inside 'edane' is 'edanalpse'.
'edanalpse' written backwards gives 'ESPLANADE'.
'where' acts as a link.
(Other definitions for esplanade that I've seen before include "Paved area at seaside resort" , "walk by sea" , "Walkway beside the seashore" , "Long level area for walking beside the sea" , "Open, level space for walks or drives" .)