An e-book edition was published by Gollancz's SF Gateway imprint on September 29, 2011 as part of a general release of de Camp's works in electronic form.

In The Castle of Iron, the authors' protagonist Harold Shea visits two such worlds, first (briefly) that of Samuel Taylor Coleridge's poem "Kubla Khan" and second that of Ludovico Ariosto's epic, the Orlando Furioso.

At that point the whole group, including police officer Pete Brodsky, are spirited away to another world, that of the Xanadu which is the subject of Samuel Taylor Coleridge's poem "Kubla Khan".

Moreover, as Ariosto's epic was a source text for Edmund Spenser's The Faerie Queene, Belphebe's mind has become confused, reverting in accord with the setting to that of her Furioso prototype, Belphagor.

Reviewing the 1950 edition, Boucher and McComas faulted the novel for weakness in plotting, but described the series as "a high point in the application of sternest intellectual logic to screwball fantasy".

[3] P. Schuyler Miller, despite finding that Castle "hasn't quite the adroitness of incongruity which marked the first book", still reviewed it favorably, saying the authors "learnedly but irreverently wreak the same havoc with Ariosto that they did with Spenser's Faerie Queene and the Norse eddas".