What some hiker turns up for? (4)
I believe the answer is:
trek
'what some hiker turns up for?' is the definition.
I can't tell whether this defines the answer.
'what some hiker' is the wordplay.
'what' becomes 'tre' (I am not sure about this - if you are sure you should believe this answer much more).
'some' indicates the central letters.
The middle letter of 'hiker' is 'k'.
'tre'+'k'='TREK'
Can you help me to learn more?
(Other definitions for trek that I've seen before include "A long arduous march" , "Slog" , "Long hike" , "A long arduous journey as in S Africa" , "Long difficult walk" .)