Nobody knows what's buried on Oak Island in Mahone Bay, nor does anybody know who put it there. Nobody knows if the Money Pit, as it has come to be called, hides the lost jewels of Marie Antoinette, though some have suggested as much.
It has been excavated sporadically - and unsuccessfully - since 1795. Some have argued that the pit holds documentary proof that Francis Bacon wrote Shakespeare's plays.
If it wasn't for booby traps (with six fatalities to date), Canada could finally pin this great mystery on Freemasons, the Knights Templar or Sir Francis Drake.
Even Captain Kidd has been fingered as a possible culprit: perhaps pirates, returning to the Caribbean by way of the Gulf Stream, stopped off in Nova Scotia to hide their booty, like dogs hiding a bone, on the edge of the northern Atlantic.
Spanish scissors and coconut fibres have been found in the pit - odd, given that the closest coconut tree is more than 2000 kilometres away.
The chairman of the Friends of Oak Island Society, Charles Barkhouse, remains unconvinced by the Captain Kidd theory.
"No pirate did this because it's a massive feat of engineering," he tells me one morning when I stop to see the island, closed to visitors though clearly visible from the shore.
"Still, somebody went to a lot of trouble to bury something of great value out there."
Maybe he's right, along with past believers such as Errol Flynn, who tried to scour the island in 1940 until he discovered that search rights already belonged to John Wayne. Maybe, on Oak Island, the two unknowns of "who" and "what" really do equal something incredible.