Koiluoto - Just large enough for a border!

The 0.03 sq km ( Around 7.5 acres of land  - Area of about 6 football fields) is split between Finland and Russia. The whole island is part of the border zone and offlimits to the public

References:

Wiki

En(x)clave Central!

Central Asia has a lot of enclaves shared between Uzbekistan, Tajikistan and Kyrgystan
This is a left over from Stalin era politics as suggested by the article

https://en.wikipedia.org/wiki/Barak,_Kyrgyzstan
https://en.wikipedia.org/wiki/Sarvan,_Tajikistan
https://en.wikipedia.org/wiki/Sokh_District
https://en.wikipedia.org/wiki/Shohimardon
https://en.wikipedia.org/wiki/Vorukh
https://en.wikipedia.org/wiki/Kayragach
https://en.wikipedia.org/wiki/Batken_Region#Enclaves_and_exclaves
https://en.wikipedia.org/wiki/Regions_of_Uzbekistan#Enclaves_and_exclaves

Seasonal Sovergnity

Pheasant Island is administered for alternating six months by France and Spain


https://en.wikipedia.org/wiki/Pheasant_Island
https://www.cntraveler.com/story/why-pheasant-island-is-sometimes-in-france-sometimes-in-spain
https://www.atlasobscura.com/places/pheasant-island

Caprivi Strip!

Caprivi Strip is a thin protrusion of Namibia. Politics never ceases to amaze one with such creations as Caprivi Strip



https://en.wikipedia.org/wiki/Caprivi_Strip

Island of Horses!

Sable Island, a thin sliver of sand belonging to Canada to a population of feral horses called "Sable Island Horse"

https://en.wikipedia.org/wiki/Sable_Island
https://en.wikipedia.org/wiki/Sable_Island_horse
http://www.bbc.com/travel/story/20150827-canadas-mysterious-fabled-sable-island

Island of Asgard

Baffin Island belonging to Canada has land forms named after characters of Norse mythology

Mount Odin
Mount Thor
Mount Asgard

https://en.wikipedia.org/wiki/Baffin_Island
https://en.wikipedia.org/wiki/Mount_Odin
https://en.wikipedia.org/wiki/Mount_Asgard
https://en.wikipedia.org/wiki/Mount_Thor

Almost One Island and The Narrowest Strait

Novaya Zemlya is "almost" a single island. Its separated into two islands Severny Island and Yuzhny Island by Matochkin Strait, which at its narrowest point is just 600 metres wide




https://en.wikipedia.org/wiki/Matochkin_Strait
https://en.wikipedia.org/wiki/Novaya_Zemlya
https://en.wikipedia.org/wiki/Severny_Island
https://en.wikipedia.org/wiki/Yuzhny_Island