The Great Galapagos Darien Expedition - Apparently.
In 1905, the British ship HMS Beagle's successor, the HMS Beagle II, set sail for the Galapagos Islands with a crew of six. However, the ship was never seen again, and it was presumed lost at sea. A treasure hunter named Tommy Thompson claimed to have found the ship's wreckage in 1971, but his claims were never verified.
The HMS Beagle II's disappearance remains one of the greatest maritime mysteries of the 20th century.