In the comics, Dream was imprisoned for 70 years (1916-1986). In order to bring the story up to the present day, this was changed to "over a hundred years." To accommodate this, the ruby is said to prolong people's lives, a trait it did not have in the comics.
The female guard (played by Naomi Cooper-Davis) is reading Stephen King's IT. This is nearly identical to the source material, with two differences: 1) The guard in the comic books is male; and 2) The book's cover in the comic books is relatively featureless, while in the Netflix series, the cover is from the novel's 2017 English language edition. Interestingly, King would later go on to write the introduction for World's End, collecting The Sandman issues #51-56.
During the introduction to the Dreaming, two portraits can be seen in the main hall. These portraits are of Geoffrey Chaucer and William Shakespeare, which is quite fitting as Dream is the King of Stories, among other things.
Bill Patterson (Dr John Hathaway) is not in the credits for this episode yet performs a vital part at the start of this series.
As the raven Jessamy enters the palace in The Dreaming, filming locations include the Great Hall of the Natural History Museum in London and Lincoln's Inn Library, another Victorian building also in London. The main hall scenes were filmed in Guildford Cathedral.