In Nova Scotia, Canada there is a mystery on Oak Island. In the late 1700s two youths set out for buried treasure on the island. They began to dig a hole that is yet to be finished despite over two hundred years of exploration. The background of the story is explained in the two videos below from the 1970s television show In Search Of...
For those who did not watch the videos here is a brief review: the hole is called the money pit. The pit has several layers of logs which slow digging. Further, at a certain depth the pit floods in with water despite having being a fair amount away from shore. Dye tests showed how dye poured into the pit end up in the ocean giving the idea that there may be tunnels that flood the pit thus acting like a defense mechanism. Finally, there is an alleged stone that says there is buried treasure (but the stone cannot be found). A short two minute movie below is a 3D diagram of the money pit along with the geography and geology of the island.
Now the mystery of Oak Island may be pirate treasure but it also could be physical geography. Geologist Robert Dunfield did not find a flood tunnel during his investigation. In fact, the underlying limestone is full of water-filled natural caves. It is possible that tide pressure could move the water around in the caves. The underground water could periodically fill the money pit because of this tidal pressure. The constant ebb and flow of the tides could force dye from the pit to the ocean. As for the timbers, natural sinkholes in that area of Canada have been known to have layers of timber at periodic distances. These sink hole will suck in debris like fibers and timer and be recapped by sand and dirt. This repeatable geographic cycle could replicate the money pit.
So is Oak Island a treasure island or are is it just natural? The money pit is probably just a natural geographic feature that was misinterpreted (if it was treasure it is the most complex vault ever with no equal). None the less it is a fascinating romantic story of history and geography.