You hear the word island, and you’re immediately ready to pack and board the next plane. But not all islands are warm, sunny paradises. Some were—or are—home to high-security prisons. Their remote locations, from which it’s nearly impossible to escape, isolates hardened criminals. Elba in Italy housed Napoleon Bonaparte. Al Capone was kept on Alcatraz in San Francisco. And Nelson Mandela spent years on Cape Town’s Robben Island.

Today, these places fascinate people. You can tour the islands, sit in a cell, and see where manual labor was performed. In some cases, you can even spend the night. If you dare.

One of the most notorious island prisons is French Guiana’s Îles du Salut. French Guiana, France’s largest overseas department, is in South America bordering Brazil, Suriname, and the Atlantic Ocean. From 1852-1953, France sent its worst criminals to the Salvation Islands, three islands just north of the mainland. Most prisoners were sent to Île Royale. Political prisoners were kept on Île du Diable. And violent prisoners were kept in solitary confinement on Île Saint-Joseph. Of the 80,000 people sent there, few left. Disease, inhumane conditions, and the guillotine took most of their lives. Those who tried to escape faced strong crosscurrents and sharks. No wonder the Îles du Salut were known as Green Hell.

Board a boat in Kourou to sail to the Îles du Salut. Île du Diable (Devil’s Island), the last island to close, is off-limits to tourists. The smallest of the three islands was first used as a leper colony. Later, political prisoners, like Captain Alfred Dreyfus, were sent here after being convicted of treason.

Île Saint-Joseph, the southernmost island, is a beautiful, haunting place. From the boat, you see white-sand beaches lined with coconut palms as you arrive. Sea turtles swim just offshore. The interior is silently eerie, though. Vines grow through decaying cells where prisoners were kept in silence and darkness. Rust is hidden by palms. The guards’ cemetery is overrun with weeds. Capuchin monkeys watch and wonder about your arrival.

By the time you reach Île Royale, you’re happy to see other people. The largest of the three islands was the prison’s administrative headquarters. Prisoners roamed the island with relative freedom. Some of the buildings are in ruins, but others have been restored. Tour the director’s house, which is now a museum. Visit the chapel and the hospital. And spend the night in the prison wardens’ mess hall. Despite your sea-view room, you’ll still be relived when the boat returns to pick you up in the morning.