Rupes Nigra

The Rupes Nigra ("Black Rock"), a phantom island, was believed to be a 33-mile-wide black rock located at the Magnetic North Pole or at the North Pole itself. It purportedly explained why all compasses point to this location. The idea came from a lost work titled Inventio Fortunata, and the island features on maps from the sixteenth and seventeenth centuries, including those of Gerardus Mercator and his successors. Mercator describes the island in a 1577 letter to John Dee:

In Jules Verne's The Adventures of Captain Hatteras (1866), the North Pole is occupied by Queen Island, created by a volcano (Mount Hatteras) in the middle of an Open Polar Sea.

...
Wikipedia