[2] When the Fortress reappears in 1958 and for the first time takes center stage in a story ("The Super-Key to Fort Superman", Action Comics #241), it is again an underground complex in a mountainous cliffside.

The general public is either unaware or at best only vaguely aware of the existence of the Fortress, and its location is kept secret from all but Superman's closest friends and allies (such as Lois Lane and Batman).

A trademark of the Fortress is that it contains a memorial statue of Jor-El and Lara, Superman's Kryptonian parents, holding a large globe of Krypton.

Doc Savage built his Fortress of Solitude in the Arctic and retreated to it alone to make new scientific or medical breakthroughs, and to store dangerous technology and other secrets.

Built into the side of a steep cliff, the Fortress was accessible through a large gold-colored door with a giant keyhole, which required an enormous key to open it.

[4] The Fortress contained an alien zoo, a giant steel diary in which Superman wrote his memoirs (using either his invulnerable finger, twin hand touch pads that record thoughts instantly, or heat vision to engrave entries into its pages), a chess-playing robot, specialized exercise equipment, a laboratory where Superman worked on various projects such as developing defenses to kryptonite, a room-sized computer, communications equipment, and rooms dedicated to all of his friends, including one for Clark Kent to fool visitors.

It also contained the Phantom Zone projector, various pieces of alien technology he had acquired on visits to other worlds, and, much like the Batcave, trophies of his past adventures.

According to Action Comics #261, Superman first established secret Fortresses in outer space and at the center of the Earth before settling on an Arctic location.

The villainous android Brainiac soon besieges the Fortress with various allies, surrounding it and the outlying territory with an impenetrable force field to keep Superman's fellow heroes from aiding him.

As Superman was forced to destroy Mxyzptlk, breaking his vow against killing, he exposes himself to gold kryptonite to permanently remove his powers and then appears to leave the Fortress to freeze to death in the Arctic cold.

[6][7] In John Byrne's 1986 Man of Steel miniseries, which re-wrote various aspects of the Superman mythos, the Clark Kent persona was described as a "Fortress of Solitude", in that it allowed him to live as the ordinary person he saw himself as and leave the world-famous superhero behind.

In Action Comics Annual #2 (1989), Superman, on a self-imposed exile to space, was entrusted with a Kryptonian artifact called the Eradicator, created by his ancestor Kem-El.

In the DC One Million series (1998), Superman's Fortress of Solitude in the 853rd Century resides within a tesseract located at the center of Earth's sun.

Superman subsequently established a new Fortress in an ancient temple on a remote village in the Cordillera del Cóndor Mountains, on the border of Ecuador and Peru.

However, Superman was able to find a temporary 'cure' for his power loss by exposing himself to kryptonite as a form of 'chemotherapy' that burned away the radiation preventing his cells from absorbing energy.

Several days after the crisis Superman uses the Fortress's medical equipment and A.I technology to do a full physical on him and discovers that as a result of Vandal's actions using Krytonite to burn out his infected cells that he is dying and has mere weeks to live.

After burying his counterpart in Smallville he returns to the Fortress and uses his heat vision to create a statue of Superman of Prime Earth to honor his fallen comrade.

The Fortress itself contains the Titanic, the Space Shuttle Columbia, and a baby Sun-Eater, as well as larger-than-life memorabilia, similar to the objects found in the Batcave.