Greek character in hotel in mountain area (5)
I believe the answer is:
alpha
'greek character' is the definition.
(letter from the Greek alphabet)
'hotel in mountain area' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' is an insertion indicator.
'mountain' becomes 'alp' (alp is a kind of mountain).
'area' becomes 'a' (maths abbreviation).
'alp'+'a'='alpa'
'h' put inside 'alpa' is 'ALPHA'.
'in' is the link.
(Other definitions for alpha that I've seen before include "Foremost" , "A for Aristophanes!" , "letter written in Greek" , "very good rating" , "letter opener" .)