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.
References
https://wikitravel.org/en/Marion_Island