After Krugar III was destroyed by a comet, a small section of land containing a museum was carried off into space and through a through a hole into a netherspace which the Curator called "Limbo". Over the years, many starships became trapped in Limbo, their pilots becoming residents of the museum, which became known as the Museum of Missing Ships. Since time did not exist there, they did not age.
In 2266, the USS Enterprise entered Limbo after slingshoting out of a cosmic storm while pursuing a Klingon battle cruiser. The Enterprise crew and the Museum's residents battled the Klingons, but the conflict abruptly ended when Spock discovered that Limbo was reaching the end of its natural cycle and would soon explode. Although the Enterprise and the Klingons were able to blast their way free in time, the inhabitants of the Museum chose to remain and die. (TOS comic: "Museum at the End of Time")