The Chagos Archipelago aka as BIOT (British Indian Ocean Territory) situated far from anywhere in the Indian Ocean - 2 groups of islands (atols) favoured by cruising sailboats are the Peros Banos islands at 5º 20.66' S x 71º51.218' E
and the Salomon Islands to the east of Banos at 5º 19.597 S x 72º14.426'E.
There are special regulations and fees regarding visits to Chagos -
Here is the email address of the office administering the Archipelago :- BIOTadmin@fco.gov.uk