Doc Fortress of Solitude

He did not explain where he had been, did not mention his "Fortress of Solitude," his rendezvous built on a rocky island deep in the arctic regions. He had been there.

It was to this spot that Doc retired periodically to brush up on the newest developments in science, psychology, medicine, engineering. This was the secret of his universal knowledge, for his periods of concentration there were long and intense.

The Fortress of Solitude had been his father's recommendation. And no one on earth knew the location of the retreat. Once there, nothing could interrupt Doc's studies and experiments.

- The Man of Bronze (1933) Chapter 2