Expedition long way off is, on return, written about (6)
I believe the answer is:
safari
'expedition' is the definition.
(I know that safari is a type of expedition)
'long way off is on return written about' is the wordplay.
'long way off' becomes 'afar' (I've seen this before).
'on return' shows that the letters should be reversed in order.
'written about' indicates putting letters inside.
'is' reversed gives 'si'.
'afar' placed within 'si' is 'SAFARI'.
(Other definitions for safari that I've seen before include "North African capital" , "Animal-viewing trip" , "Expedition to see animals" , "Overland journey by hunters" , "Long expedition" .)