Shutter Island does not exist; there are no Shutter Islands in the entire United States, nor am I aware of any insane asylums that have ever existed on isolated American islands. There have been a number of prison or detention islands, though none quite resembled the fictional Shutter Island physically.

The last unbridged prison island in the US is McNeil Island, Washington. It houses both a large state prison complex, and a program of civil detention for sexual predators, who are essentially being confined as mentally ill.

Steep-sided, flat-topped, gloomy islands like the one in the movie are relatively rare. For physical similarity, one might go with Anacapa, in the Channel Islands of California:

(Anacapa image courtesy Scubacayman88, Flickr)

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For a small state with a short coastline, it possesses a nice assortment of islands, both on its dramatic coastline and in lakes. Many are embellished with historic sites, especially monasteries.

Montenegrin island superlatives
Largest island — There are two candidates of virtually identical size, both about 1.9 square miles / 4.8 square km.

• Ada is a delta island on the southeast border with Albania.
• Vranjina, a monastery island on the northwest side of Lake Skadar, is formed by the lake and the incoming Moraca river.  Vranjina is Montenegro’s largest freshwater island.

Largest sea island — Sveti Nikola is about 36 hectares / 90 acres.

Tallest island — Vranjina rises 296 meters or about 971 feet above Lake Skadar.

Tallest sea island — Sveti Nikola is 121 meters or about 397 feet tall. Second-tallest is Sveti Marko, at 36 meters or about 118 feet.

Sea islands
Montenegro has several sea islands of note in the Boka Kotorska:

• Prevlaka — bridged; 13th century monastery ruins
• Sveti Marko — off Tivat; has a Club Med
• Otok — islet off Sveti Marko with a monastery
• Gospa od Skrpjela — artificial islet off Perast with notable church
• Sveti Dorde — another islet off Perast, site of a Benedictine Abbey

Sveti Nikola is in the Adriatic off Budva, and has church ruins and an endemic species of lilly; boat tours go here.

The most famous Montenegrin “island” is not an island at all: Sveti Stefan is lovely and walled, but now a peninsula.

Lake islands
Montenegro’s lakes are dominated by Lake Skadar (Skadarsko Jezero), in the southeast. It seems to have 50 or more islands; a number are listed here. Monastic islands include Vranjina, Starcevo, Beska, and Sveti Dorde. Skadar also has a prison islet, Grmozur.

Montenegro also has islands in reservoir lakes, including a concentration near the city of Niksic.
[Montenegrin islands, Montenegrin geography]