At the end of the episode Clark's childhood tree house was named "Fortress of Solitude". This was the name of Superman's headquarters in DC Comics. The Fortress made its first appearance in issue May-June 1949 and is traditionally said to be located in the Arctic. Since the series was supposed to be about Clark, and Superman was his secret identity, and not the other way around as in the comic series, the Fortress was not needed.
David Warner plays Superman's biological father Jor-El in this episode. He previously co-starred with Susannah York in A Christmas Carol (1984) in which they played Bob Cratchit and his wife. York also played Lara Lor-Van, Jor-El's wife and Superman's biological mother, in Superman (1978), Superman II (1980) and Superman IV: The Quest for Peace (1987).