Yearn extremely to visit the ends of the earth: one reaches a group of islands (9)
I believe the answer is:
polynesia
'group of islands' is the definition.
'polynesia' can be an answer for 'islands' (I've seen this before). I am not sure about the 'group of' bit.
'yearn extremely to visit the ends of the earth one reaches a' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'to visit' indicates putting letters inside.
'the ends of the earth' becomes 'poles' (I've seen this in another clue).
'one reaches' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'yearn' with its centre removed is 'yn'.
'yn' put into 'poles' is 'polynes'.
'polynes'+'i'+'a'='POLYNESIA'
Can you help me to learn more?
(Other definitions for polynesia that I've seen before include "part embracing South Pacific" , "large group of islands" , "Extensive group of Pacific islands" , "Antipodeans around here" , "Pacific island group" .)