THOR (1962) #386

Thor goes on one final quest before returning to Earth; He follows a griffin-like creature through a portal to Avalon; There he battles Leir after a misunderstanding until Leir spots the creature as well; With the help of Hogun, they drive the creature back to Asgard, where it is defeated by Fandral and Volstagg; Thor goes to leave for Earth, but the warning comes too late; Asgard is adrift without Bifrost to anchor it, and Thor has transported himself into the depths of airless space.