Top again, a remarkable South American region (9)
I believe the answer is:
patagonia
'south american region' is the definition.
(I've seen this before)
'top again a remarkable' is the wordplay.
'remarkable' indicates anagramming the letters.
'top'+'again'+'a'='topagaina'
'topagaina' with letters rearranged gives 'PATAGONIA'.
(Other definitions for patagonia that I've seen before include "part of South America" , "far-off land" , "Region of southern Argentina and Chile" , "Region of South America" , "Craggy region" .)