Is climbing in a rough mountainous area (5)
I believe the answer is:
sinai
'mountainous area' is the definition.
'Sinai' can be an answer for 'area' (Sinai is an example). I'm unsure of the 'mountainous' bit.
'is climbing in a rough' is the wordplay.
'climbing' says the letters should be written in reverse (in a down clue, letters climb up).
'rough' is an anagram indicator (a rough or broken ordering of the letters).
'is' reversed gives 'si'.
'in'+'a'='ina'
'ina' anagrammed gives 'nai'.
'si'+'nai'='SINAI'
Can you help me to learn more?
(Other definitions for sinai that I've seen before include "11 Across peninsula" , "Law handed down here" , "Mountain in Egypt" , "desert area" , "Mount where Moses received God's law" .)