After a little research, I think we’re onto something here. I Googled ‘Bermuda 500kg Gold Bar’ and the first hit was an old pirate map with ‘X Marks the Spot’ showing pretty much the same location. I confirmed this by comparison with the 1958 edition of “My First Atlas (in Colour)”. Just need to solve the riddle that was written on the map.
My first is in pirate, but not in gold.
My second in treasure, but not in behold.
My third is in loot, but not in in plunder.
My fourth is in look, but not in wonder.
The last of my letters is from a Brazilian
Who promises that he can make you a million.
He can find you an ingot the size of a fridge.
He has cloven hooves and lives under a bridge.