The Fortress of Solitude is the place of solace and occasional headquarters for Superman in DC Comics. Its predecessor, Superman's "Secret Citadel", first appeared in Superman #17, where it was said to be built into a mountain on the outskirts of Metropolis. By issue #58 (May–June 1949) it is referred to as the Fortress of Solitude, seems at a glance to be a freestanding castle, and is said to be located in a "polar waste." However, when the Fortress finally reappears in 1958 and for the first time takes center stage in a story ("The Super-Key to Fort Superman", Action Comics #241), it was once again an underground complex in a mountainous cliffside.