The Super-Key to Fort Superman was a comic book story appearing in Action Comics #241, in June of 1958. It featured the first appearance of the Fortress of Solitude as it's known today, although an earlier version had appeared in the Golden Age.
Superman while visiting the fortress of solitude in an attempt to relax, discovers that there is an intruder within the fortress. Superman attempts to seal the entrance, but learns that the intruder is still there. A cave-in occurs, which seals him in with a kryptonite rock. The intruder then reveals himself as Batman. Superman starts to laugh, because he knows that the kryptonite is fake. He tells Batman that he used it in an attempt to get Batman to reveal himself. Superman's friends then celebrate his anniversary of arrival on earth.
This story is reprinted in Superman Annual 1, World's Finest Comics 173, Best of DC 16, Greatest Superman stories ever told Giant Superman Annual 1, Superman: The Man of Tomorrow Archives Vol. 1, and Showcase Presents: Superman Vol 1.