National park established around fantastically green island (9)
I believe the answer is:
serengeti
'national park' is the definition.
(I've seen this before)
'established around fantastically green island' is the wordplay.
'established' becomes 'set' (set can mean established or agreed upon).
'around' indicates putting letters inside.
'fantastically' indicates anagramming the letters (a fantastical ordering of the letters).
'island' becomes 'i' (geographical abbreviation).
'green' is an anagram of 'renge'.
'set' going around 'renge' is 'serenget'.
'serenget'+'i'='SERENGETI'
(Other definitions for serengeti that I've seen before include "Wildlife-rich region of Africa" , "Tanzanian national park area" , "Tiger seen in Tanzania's great National Park" , "Vast plain" , "African plain noted for wildlife" .)