Most dangerous, heading off to mountain (7)
I believe the answer is:
everest
'mountain' is the definition.
(I've seen this before)
'most dangerous heading off' is the wordplay.
'most dangerous' becomes 'severest' (I've seen this before).
'heading off' means to remove the first letter.
'severest' with its first letter taken off is 'EVEREST'.
'to' is the link.
(Other definitions for everest that I've seen before include "Highest Himalayan mountain" , "Himalayan peak" , "High mountain" , "Great achievement" , "Tallest mountain ..." .)