I got thinking about this because of the metal detecting coin find topic, which naturally made me think of a story I'd heard from an English-born guy who paid for his vacation in Gibraltar by free-diving for lost Rolexes off Gibraltar (he was also a metal detectorist, and a little shady). And the video linked below contributed to the idea for this topic, which is really a connection with prehistoric navigation.
Now Hear This: Scarlatti Man Out of Time
