Information about large highland valley (4)
I believe the answer is:
glen
'highland valley' is the definition.
(I've seen this in another clue)
'information about large' is the wordplay.
'information' becomes 'gen' (gen can informally mean information).
'about' means one lot of letters goes inside another.
'large' becomes 'L' (eg in clothes sizes).
'gen' placed around 'l' is 'GLEN'.
(Other definitions for glen that I've seen before include "Scottish mountain valley" , "Long narrow valley in Scotland" , "Narrow valley with a stream" , "Narrow secluded valley in mountains" , "Valley, dale" .)