Truck going round cold region up north (6)
I believe the answer is:
arctic
'region up north' is the definition.
(I've seen this before)
'truck going round cold' is the wordplay.
'truck' becomes 'artic' (short for articulated lorry).
'going round' means one lot of letters goes inside another (some letters go around others).
'cold' becomes 'C' (abbreviation, eg on taps).
'artic' enclosing 'c' is 'ARCTIC'.
(Other definitions for arctic that I've seen before include "Region around the North Pole" , "Poplar region" , "Freezing cold like North Pole" , "Of North polar regions" , "Area centred on the North Pole" .)