Hannibal's challenge (4)
I believe the answer is:
alps
'hannibal's challenge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alps that I've seen before include "high points" , "Mountain system, highest peak Mont Blanc" , "South-central European mountain system" , "high areas" , "Laps around mountains" .)