Sprayed between Sweden and Finland, the autonomous Aland Islands are a picturesque archipelago once part of Russia and demilitarised since 1856.
But the region's unique status is the object of intense debate since Russia's invasion of Ukraine rattled neighbouring Finland into applying for NATO membership in May.
Under international treaties signed after the Crimean War, no troops or fortifications can be placed on the strategic Baltic Sea islands.
"It is the Achilles' heel of Finland's defence," Alpo Rusi, a professor and former presidential advisor, told AFP.
Home to about 30,000 mostly Swedish-speaking Finns, the area is characterised by rocky islands, lush green forests, old stone churches and wooden architecture -- all under the watchful eye of a Russian consulate.
"We have always thought, 'Who would want to attack us when we have nothing worth taking?'," 81-year-old Ulf Grussner told AFP.
"But that has changed with Putin's war on Ukraine", said the pensioner, one of many here who want Aland to remain demilitarised.
In June, a poll showed 58 percent of Finns would approve of a military presence on Aland, which celebrated the 100th anniversary of its autonomy on Thursday.
"There is concern over whether Finland could react fast enough militarily in the event of a sudden intrusion on Aland," Rusi said.
Armies wrestled for control of the archipelago in both World Wars.
"Why should we trust the idea ... that troops would not rush to control Aland as fast as possible," said Charly Salonius-Pasternak, a researcher at the Finnish Institute of International Affairs.
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