Somewhat reckless plan to climb mountains (4)
I believe the answer is:
alps
'mountains' is the definition.
(European mountain range)
'somewhat reckless plan to climb' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'to climb' says the letters should be written backwards (I've seen 'climbs' mean this).
'spla' is hidden in the letters of 'reckless plan'.
'spla' backwards is 'ALPS'.
(Other definitions for alps that I've seen before include "High mountains" , "high areas" , "European mountain chain" , "Pals put on the mountains" , "European mountains" .)