Although it lasted only 39 issues, from March 1939-October 1943, Unknown Worlds is one of the more renowned magazines in the history of speculative fiction. Isaac Asimov spoke for many of the readers of the time when he commented, "for us who knew it in its glory, it can never really die. . . . there was never anything like it before and never anything like it since". (7, The Unknown) The only fantasy magazines in the early 40s were Weird Tales and Unknown, with the latter consistently having better content. In fact, before a wartime paper shortage closed it down, it's remarkable how many fantasy classics the magazine published, in genres as varied as horror, humorous fantasy, urban fantasy, and sword and sorcery.

John W. Campbell wanted Unknown to serve as a fantasy companion for Astounding, because writers sometimes submitted good stories that weren't techno-focused enough for the hard sf magazine. The same stable of writers submitted to both magazines, and Unknown's fiction was just as strong as the work going into Astounding.

What made Unknown's brand of fantasy unique? Unknown attempted to combine the extrapolation and idea-focus of science fiction with fantasy; contrasting it with its rival Weird Tales, which published dark, weird fiction (thus the name), often with a strong element of horror. Although Unknown certainly published its share of dark stories, its stress on ideas and logic allowed free rein for writers such as Fritz Leiber or L. Sprague de Camp to innovate and take fantasy in new directions.

In Astounding, Campbell required the writers to base their stories on plausible scientific extrapolation; in Unknown he gave them the freedom to use the supernatural, magic, and absurd premises, but once they established their premise they were expected to logically portray the consequences. Unknown published fantasy with the same rigor as Astounding-style sf, melding many of the better traits of both genres.

L. Sprague de Camp, one of the magazine's most prolific contributors, wrote 10 of the 40 novels published in Unknown, and his work encapsulated the magazine's approach to fantasy. In "The Gnarly Man" he describes an immortal Neanderthal who survives until the 20th century. Once you accept the initial premise, the way the Neanderthal lives in modern America—as a carnival attraction—and the ways that people react to him—as a strange hairy man (some women even find him virile)—makes perfect sense. It was common for an Unknown story to realistically portray utterly preposterous or outrageous fantastic situations.

Lest Darkness Fall is a 1939 novel in which a 20th century American is transported via time travel to 6th-century Italy. The plot is obviously inspired by Twain's A Connecticut Yankee in King Arthur's Court, but de Camp's novel provides a more convincing portrayal of Dark Ages Italy than Twain's Arthurian England, and his description of technology and its effect on society is more plausible. While dramatizing the protagonist's humorous misadventures, the novel raises a serious theme: can one man change history for the better? The protagonist Padway is a historian who knows the political details of the time and the local dialects, and he has arrived at a period when the Roman Empire is collapsing, and civilization sinking into the Dark Ages. Padway tries to preserve civilization by developing technology such as the printing press, semaphore towers, postage services, and modern political organizing. The book realistically portrays the difficulty of integrating technology into a medieval society. Many of the characters find it difficult to understand the purpose of Padway's new technologies: one person assumes his printing press must be a new torture device. Lest Darkness Fall is an Unknown story because the struggles Padway faces are all idea-focused: he doesn't escape his problems with hack and slash sword play like Conan (which is not to disparage Conan—I sometimes like hack and slash.)

De Camp also co-wrote a series of Harold Shea stories with Fletcher Pratt. The bored research psychologist Harold Shea and an older scientist, Reed Chalmers, create a formula that allows them to journey to alternate worlds. In humorous, clever stories they enter the world of the Norse gods, Spenser's Faerie Queen, the Xanadu of Coleridge's poem "Kubla Khan," and the universe of Aristo's Renaissance epic Orlando Furioso. Each world that Shea enters has its own laws and logically extrapolated (once you accept the magic) ways of functioning. Shea discovers that matches and his revolver do not work in the Norse world, but he can cast spells so long as he follows the laws of magic: contagion and similarity as described in Frazer's "The Golden Bough." The portrayal of women in the stories is dated—the female lead is a flat character who largely exists to be rescued—but other than that the Shea series holds up remarkably well.

Robert Heinlein encapsulated the Unknown approach to speculative fiction with his 1940 story "The Devil Makes the Law!", which portrayed an alternate world where magic works by laws as predictable as the scientific method, turning magic into an unavoidable bureaucracy. The magic is so rationalized in the story it reads like SF. In "The Unpleasant Profession of Jonathan Hoag," a man discovers he's the flawed universe's art critic. In "They"—a work of solipsism as intense as anything by Philip K. Dick—a man is convinced the world is nothing but a puppet show.

L. Ron Hubbard was also a frequent contributor, publishing seven novels in Unknown; his work often involved transporting characters into dreamworlds of their own creation. "Typewriter in the Sky" is the humorous story of Mike de Wolf, who is visiting his friend Horace Hackett, a pulp fiction writer desperately scrambling for ideas because he has a novel deadline in a few days (for a pulp writer like Hubbard or his alter-ego Hackett, writing a novel in a few days was not unusual). Deriving inspiration from what's close at hand, Hackett transforms his friend de Wolf into the villain Miguel de Lobo, who attempts to defeat the English in the 17th century Caribbean. Like a typical pulp villain, de Lobo is doomed to lose the war, and the woman he loves to the noble hero. After de Wolf goes to sleep, he wakes up in the world of the story; he is no longer just the inspiration for the villain, he has somehow been transported into Hackett's novel and become de Lobo, spouting pulp dialogue and plotting intrigues.

Hubbard explores the premises of the story in great detail. When Hackett is writing about him, de Lobo hears a typewriter in the sky, and has to follow the actions and vocalize the dialogue written by his hack novelist friend. When Hackett isn't writing about him—when he's depicting the actions of the hero—de Lobo has free will and can try to change his inevitable defeat and loss of the heroine. When de Wolf succeeds at changing events and throwing the story off track, Hackett crumples up those pages and rewrites to push the novel to its predetermined ending. Hackett explains the shifts of the narrative as an example of the characters and stories acting on their own and taking the story in unexpected directions.

Hubbard's novel Fear is probably the best horror novel published in Unknown; it depicts a skeptical college professor tormented by demons and transported into a horrific dreamworld. Whereas "Typewriter in the Sky" is humorous and witty, Fear is a dark tale in which the protagonist comes to believe that he is the only person in the world and that existence is a conspiracy against him. The novel develops a solipsistic premise as effectively as Heinlein's "They." The conclusion reveals that the demons are the evil within his unconscious and a result of repressed memories. These two novels demonstrate that Hubbard could write before he entered the more lucrative world of cults.

Quite a bit of powerful, well-thought out horror was published in Unknown. Jack Williamson's classic werewolf story "Darker than You Think" gave a scientific explanation for werewolves, which were humans on a different evolutionary path. Conjure Wife, by Fritz Leiber, deals with conspiracies and the notion that the universe is secretly very different that we think. In the novel all women are witches, a fact that most of their husbands don't know; the careers of the male academics depend on the magical battles between their wives. Leiber also wrote "Smoke Ghost," one of the first great modern ghost stories, which depicts an elemental that grows out of a modern city and demands worship. Theodore Sturgeon's widely anthologized "It" makes us care about a small family, and then threatens them with a supernatural menace (a formula Stephen King has used quite a bit in recent years). Manly Wade Wellman's "When It was Moonlight" is a historical horror story, featuring Edgar Allan Poe's encounter with a vampire, an encounter that supposedly inspired many of Poe's stories such as "A Premature Burial".

Fritz Leiber also created the literate Fafhrd and Grey Mouser Sword and Sorcery series. Like most of the great teams throughout literature and film, the duo both contrast with, and complement one another physically and mentally. Fafhrd is a seven-foot-tall, brawny, highly intelligent barbarian (vastly different from Conan), whereas the Grey Mouser is a short, clever, rapier-wielding thief. The excesses of one character may drive one part of a story, to be followed by the quirks of the other in a different part of the narrative. Leiber develops the city of Lankhmar in sleazy, colorful detail with its Thieves Guild, Street of the Gods, backstabbing intrigue, and wizards. The heroes use their swords and combat prowess, but tend to defeat powerful antagonists—such as Death—through their wit. Leiber also used innovative narrative techniques in the stories, such as using Lankhmar as a collective narrator brooding on the heroes in "The Bleak Shore," or a play within the play (or story) in "Thieves' House," a narrative technique lifted from Shakespeare (Leiber spent some time working as a Shakespearean actor).

Lester del Rey made some impressive contributions to the magazine, including "The Pipes of Pan." In this tale, the last worshipper of Pan dies, and when a god loses his/her last worshipper s/he either dies or becomes a human. Pan is suddenly placed, virtually penniless and hapless, in modern America. The story impresses because it deposits the god realistically in 40s America, and portrays his struggles to disguise himself as a human, make a living, and pay for meals at cheap diners. Pan eventually uses his musical talent to become a jazz musician, cultivating fans that worship his musical talent.

Some notable short stories appearing in the magazine include "Prescience" by Nelson S. Bond, which describes a psychologist helping a female patient with precognitive dreams: the psychologist's self-satisfied rationalism and close-mindness results in disaster. In Theodore Sturgeon's "Yesterday was Monday" the protagonist discovers that the entire universe is just an elaborate stage set when he wanders into the wrong day, and the wrong stage. The story again—like Hubbard's and Heinlein's—deals with the themes of solipsism and conspiracy.

Henry Kuttner wrote extensively for Unknown just as he did for virtually every pulp publication. His story "The Misguided Halo" is a widely anthologized piece, which starts with the premise: what if a modern man suddenly awakened with a halo? Once you accept that premise, the story realistically portrays how people react to the halo. The story develops that theme fairly well, but is only an average effort for the magazine.

A number of stories from Unknown depict the inhabitants of Faerie intruding into the modern age. These types of tales are known as urban fantasy today, and may have been overdone in recent years—see Charles de Lint—but at the time the combination of the mundane and the marvelous was striking. H.L. Gold's "The Trouble with Water" describes a henpecked husband—who just wants to get away from his wife and daughter for an afternoon of fishing—angering a water gnome. In "The Refugees" by Frank Belknap Long, Irish elves flee WWII—they find the bombings disconcerting—and try to find a place to live in modern America. "A Gnome There Was" portrays a naïve, idealistic labor organizer transported to Gnome mines, who then convinces the Gnomes to strike.

Another common technique for Unknown writers was to take an old idea and give it an unusual twist. "Doubled and Redoubled" by Malcolm Jameson depicts a man who has to live the same day over and over again, similar to Bill Murray in Groundhog Day, turning the basic idea into an interesting character study. Anthony Boucher’s tongue-in-cheek story "Snulbug" combines two fairly well-worn themes: calling up a demon from hell and a newspaper from the future, but gives the ideas some clever twists as the narrator discovers that it's impossible to change the future. In "Armageddon" Frederic Brown turns the apocalypse into a joke instead of the more standard horror story.

There are certainly a number of stories published in the magazine that appear dated, or uninspired. Theodore Sturgeon is one of speculative fiction's finest writers, but his novella "The Hag Seleen" is not up to the quality of his best work. Sturgeon's story offers an evocative portrait of a Louisiana swamp, and the characterization of the endangered family is better than most pulp fiction, but the evil Cajun witch is a terrible concoction, spouting dialect like this: "Seleen belong this swamp. Wan man make p'tit cabane in bayou, Seleen l'enchane" (356, Unknown Worlds: Tales from Beyond). This dialogue is worse than the Cajun character Gambit in the X-men; it make me wan' read diff'rnt story, mon cherie.

Even some of the famous Unknown stories don't appeal as much as they once did. Alfred Bester—again generally a brilliant writer—published "Hell is Forever." The basic concept relies on the common Unknown trick of putting a new spin on an old idea, "making a deal with the devil." A demon offers a group of unappealing, decadent aristocrats their heart's desire, allowing them to create the world they want to live in. Each character enters a different world; although all of them are granted their heart's desire, the flaws and corruptions in their respective characters cause each of them to create his/her own hell. The tale is certainly an Unknown story: from its detailed elaboration of its conceit, to the clever uses of solipsism, but it is much too long considering the hackneyed theme. Also, it's rather predictable: the characters are assholes, they're making a deal with the devil, so they come to a bad end.

While researching this article, I reread a great deal of the Unknown corpus, and one thing that struck—and surprised me—was how much themes of solipsism and paranoia color the horror stories, such as Hubbard's "They," Sturgeon's "It," Leiber's Conjure Wife, and Bester's "Hell is Forever." I don't want to overemphasize that observation because many of the stories are light and clever in tone, but the stories were written during WWII, a war the allies did not know they were going to win, and those pressures and concerns affected the writing. Although the stories avoided direct commentary on politics—which was true of Astounding as well—the cultural zeitgeist and the darkness sweeping Europe were part of the magazine.

Overall, Unknown focused on cleverness and logical extrapolation, and created an idea-focused fantasy version of Astounding. What remains most impressive about Unknown stories is the ideas and intelligence that went into the fiction; these stories are definitely not the cliché-ridden Tolkien clones that infest too many fantasy shelves today.

The best way to experience Unknown fiction is to pick up a few anthologies and novels (see the Bibliography). The original magazines are expensive, generally running $10 or $20 apiece. Buying the entire run—if you could find it—would cost several thousand dollars.

Does the Unknown tradition continue, or is it forgotten and moldering with the pulp magazines that published it? Recently, Michael Swanwick published some Unknown-style fantasy: The Iron Dragon's Daughter and The Dragons of Babel, which depict industrialization and mechanical war dragons in Faerie. The novels' portrayal of logically extrapolated economies in Faerie is reminiscent of Unknown. Steampunk combines fantasy and science fiction, showing the grit, grind, and logic of a fantasy world; a good example would be Ken MacLeod's story "Light." Neil Gaiman's American Gods portrays a group of gods wandering the landscape of modern America, its combination of the mundane and the marvelous reminiscent of "The Pipes of Pan." Gene Wolfe's Book of the New Sun tetralogy is Unknown-style science fantasy, with the magical events rationalized as SF elements such as time travel, telepathy, and telekinesis. Randall Garrett's Lord Darcy series was directly inspired by Unknown; it depicted an alternate world with magic that worked according to logical, well-extrapolated scientific laws. It's possible some of these writers may not know the magazine that originally published Unknown-style fiction, but enough of the stories from the magazine are still read to continue an important, undying tradition that threads its way through a great deal of powerful speculative fiction.