I understand you need some adventure - go rock climbing (5)
I believe the answer is:
roger
'i understand' is the definition.
(I've seen this before)
'some adventure go rock climbing' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'climbing' is a reversal indicator (in a down clue, letters climb up).
'regor' is hidden within 'adventure go rock'.
'regor' reversed gives 'ROGER'.
'you need' is the link.
(Other definitions for roger that I've seen before include "Sir - de Coverley, English country dance" , "R in telecommunications" , "Boy's name - I will do what you say" , "Chap" , "Boy's name - message understood" .)