The Galápagos are better known for their sea lions and penguins than postal service. But the island of Floreana operates a unique stampless system of sending mail from one of the world’s most diverse, uninhabited areas.

Long before ecotourists annexed the remote islands off Ecuador’s coast, it was a pit stop for 18th-century whalers traversing the oceans. After months or even years on the job, the homesick seamen came up with an ingenious system of getting letters to their families. They erected a barrel on Floreana Island and left their mail for sailors on passing ships to deliver.

The first mention of the post office appears in the Journal of a Cruise, Captain David Porter’s account of his 1813 trip to the Galápagos, according to a timeline crafted by John Woram, author of Charles Darwin Slept Here. In his book, Porter recalls a crew member returning with papers “taken from a box which he found nailed to a pot, over which was a black sign, on which was painted Hathaway’s Postoffice.”

Twenty-five years later, another explorer documented the practice of bottling notes and leaving them to be taken back to America by fishing vessels. Those same fishermen “would never fail, before their departure, to touch at this island to take on a supply of tortoises.” The consumption of giant sea tortoises during this period is one of the reasons why Charles Darwin found none left on Floreana Island when he arrived in 1835.

This unconventional system has persisted into the 21st century. Today, thousands of letters pass through Post Office Bay. Tour groups often stop at the island to explore the ancient lava caves and to pick up and drop off postcards.

The simple wooden barrel is covered in notes and keepsakes from travelers passing through in what resembles a glorified birdhouse. The origins of the first barrel are opaque, but it may have come from a crew in the 1890s. Since then, the barrel has been replaced by visiting vessels from around the world. Over the years, driftwood bearing painted names and dates has been piled around the site to commemorate long-ago letter deliveries.

After visitors sift through the mail and collect letters going to a home near their final destination, they can mail or, preferably, hand-deliver letters to the recipients. Tour guides are known to say that slapping a stamp on the letter and dropping it in a mailbox is cheating—though the 18th-century whalers likely wouldn’t object to any method that saw their letters delivered.”