Be sure to wander in the darkness (6)
I believe the answer is:
erebus
'darkness' is the definition.
(personification of darkness in Greek myth)
'be sure to wander' is the wordplay.
'to wander' indicates an anagram.
'be'+'sure'='besure'
'besure' with letters rearranged gives 'EREBUS'.
'in the' is the link.
(Other definitions for erebus that I've seen before include "Volcanic mountain in Antarctica" , "Dark and gloomy cavern between earth and Hades." , "In place of darkness" , "Antarctic volcano; region between earth and Hades" , "Be sure (anag) - Greek god" .)