The sub-Antarctic Prince Edward Island Group consists of; Marion Island (19km long 12 km wide) and Prince Edward Island (10 km long and 6.5km wide). These islands are approximately 1920 km south-east of Cape Town and are politically part of South Africa. The only way to travel to Marion Island is on board a South African research vessel. Research team members remain on the island for 14 months, but it is also possible to visit the island as part of the relief team.
Geolocation
-46° 50' 27.1296", 37° 47' 15.3006"
References

https://wikitravel.org/en/Marion_Island