Sarah travelled a wilderness (6)
I believe the answer is:
sahara
'wilderness' is the definition.
(thesaurus)
'sarah travelled a' is the wordplay.
'travelled' indicates anagramming the letters.
'sarah' with letters rearranged gives 'sahar'.
'sahar'+'a'='SAHARA'
(Other definitions for sahara that I've seen before include "Hottest desert" , "North African desert" , "World's largest desert" , "Great desert in N Africa" , "About 3,500,000 square miles of Africa" .)