Perhaps in its very nature, the sci-fi genre is relatively complex: short stories, novels, TV series and films that make up speculative fiction kind of relies on detailed expository passages to build far-flung futures, reality-bending premises, and wild tales set in a galaxy far, far away.

Whether the story is set on an alien world populated by creatures markedly different from human beings, in a future separated by centuries or eons from the present–in which apes evolve from MAN??— or bending the very ideas that constitute our understanding of reality, sci-fi stories require complex set-ups to construct a believable world that’s very different from what we consider our own.

In short, the sci-fi genre inherently also allows for its stories to become quite complex. Time travel stories thrive on this sort of tangled knot complexity, while depending on the story other elements may be willfully obtuse to promote an air of mystery–or maybe to purposely disorient in the viewer to allow for a more impactful story to be related.

That said, here are 10 sci-fi films that are–by design–purposely complex, either in order to replicate the extraordinary events occurring in the story, to mirror the effect an advanced technology that’s in use as part of the plot, or simply to keep the viewer in the dark about unknowable creatures and the nearly inexplicable that happens during the film. For sci-fi fans that already appreciate the worlds that can be built in the genre, these films are delightful knots to untie and worlds that reveal layers like Matryoshka dolls.

10. Predestination (2014)

Time travel stories are some of the oldest in the science fiction genre. In fact, H.G. Wells’ The Time Machine is often cited as the first sci-fi story ever published. And it’s a hardy vehicle for a story: almost anything can happen in a time travel story. Your character can travel from the past to the present to the future instantaneously to any geographical location. There’s literally no limit to the kinds of stories that can be told using this device.

2014’s Predestination seems to set out to push the limits of what a time travel story can allow. Based on Robert Heinlein’s classic 1959 short story “–All You Zombies–,” the film follows the efforts of a Temporal Agent–whose job it is to travel through time to stop major disasters from occurring–who begins to use his ability to ensure his own career’s success. Along the way and through various points in time he meets a number of enigmatic characters while also chasing an elusive terrorist who also seems to be able to travel through time.

There is no way to speak further about this movie without spoiling the massively surprising and mind-bending nature of the narrative, but suffice to say you have never seen a movie like this before. Its intricate and elusive plot unfurls to such a surprising conclusion that you’ll be thinking about how it all worked out long after the film ends. It’s a fantastically complex sci-fi film that features paradoxes, self-closed loops, and how living life as a time traveler can be even more confusing than you think.

9. The Man Who Fell To Earth (1976)

An alien, who calls himself Thomas Newton, comes to Earth to find a way to save his planet and family, who are dying without available water. He uses his advanced knowledge to create technology that makes him one of the richest men on Earth, which was supposed to finance his return to his planet. Instead, he fakes a launch to give his family the illusion that he’s returning and stays on Earth, eventually dissolving into alcoholism.

When he’s turned into the government after people close to him realize he’s an alien, he’s experimented on and held captive for years–until he awakes one day and realizes nobody’s guarding him anymore. He continues his life, now a somewhat naturalized human, drinking himself into a stupor.

This is a straightforward summary of a decidedly not straightforward film. Nicolas Roeg–an iconoclastic director whose films often challenged linear narratives–may have made his masterpiece with The Man Who Fell to Earth. Between scenes, the narrative may jump a number of years with no warning or expository dialogue, only having characters age subtly to hint that time has passed.

This is made even more difficult to follow since Thomas Newton–played brilliantly by David Bowie–doesn’t age, which is one of his traits that eventually gives him away. Preferring mosaic-like collages of images and stream-of-consciousness editing to tell the story, The Man Who Fell to Earth may take a few screenings before a first-time viewer understands its structure and story–but it’s well worth the extra effort for one of the best sci-fi films ever made.

8. The Fountain (2006)

Darren Aronofsky has made some bewildering films in his career from the start, with his complex low-budget masterpiece Pi. But The Fountain, a sprawling metaphysical look at the nature of life, history, and mortality, may be his most confounding. Starring Hugh Jackman as a man that’s shown living three lives throughout history, and in all of them obsessed with finding immortality, The Fountain doesn’t provide any easy answers to the gigantic questions it poses.

Instead, we see Hugh Jackman as a conquistador exploring the New World for the fountain of youth; Hugh Jackman as a 21st century doctor trying in vain to find a cure for his wife’s cancer, ignoring the time they have left to focus on his work; and Hugh jackman as the doctor now as a space traveler hundred of years in the future, wandering the cosmos in a bubble, travelling to a nebula in deep space.

The intertwining, mirroring stories told across this wide timeline echo and deepen the meaning of the film until its climax seemingly answers all of the questions all three stories have posed–but it’s not straightforward. Instead, this complex sci-fi film rooted in magical realism explores the nature of obsession, fear of death, and desire for immortality obliquely. But perhaps a film like this that addresses such large, difficult concepts like these in a straightforward manner–instead, The Fountain provides a vague map to navigate by.

7. Coherence (2013)

Time travel can make for a complex sci-fi film, but what about alternate dimensions that collide together? As Coherence shows, it can certainly ruin a dinner party–and your reality. On the night of a comet that burns bright in the sky, an informal gathering between friends and ex-lovers descends into chaos after the power goes out and some parts of the group leave the house to explore the only other on the block that has power. They return and explain that they and left a note on the door of the other house. Then they find a note on their door–written by one of them.

Eventually, the group figure out that the other house is another version of themselves, and the comet must have opened a portal to another dimension. But are the people who returned the same people that left? And how many more alternate realities are there occurring?

Coherence is a low-budget sci-fi film that accomplishes its complex story with clever writing and the ability of the actors to sell the confusion and underlying sinister motives they (or at least a version of them) have as the film heads towards its conclusion. It may leave you confused, but there can be only one conclusion to the movie–even if there’s more than one of the same person extant in reality.

6. Upstream Color (2013)

Shane Carruth’s follow-up feature to Primer, Upstream Color, continued his talent for experimental narrative structure, this time following the disastrous aftermath in two people’s lives after they are drugged by a mysterious parasite by criminals that put them into highly suggestive hypnotic states, in which they were directed to hand over all their money and possessions, waking up later with no memory as to what has occurred.

Of course, the film itself isn’t that straightforward. Interspersed with glimpses of the two victims are vague scenes of a pig farmer, who harvests the organism from one of the victims that he injects in one of his pig, as he records sounds of nature. One victim, a young woman, seemingly telepathically connects with a young man and the two begin a relationship, only for both to realize they were victims of the same hypnotic parasite.

While Primer was confusing, Upstream Color is often bewildering. Beautifully shot and intriguing, Carruth still made an increasingly obscured narrative that never clears up, even at the end. Another puzzle to be sorted and put together in the viewer’s mind, Upstream Color is a movie about cycles–cycles of life, behavior, and acceptance. An elliptical movie that moves perpendicular in time, this sci-fi film is a fascinating and mysterious work of art.

5. Primer (2004)

By their very nature, time travel movies are going to be inherently complex. Keeping track of a character’s position in time, and the consequences of time travel, multiply with every new trip to the past or future that takes place in a story. But Primer went a few steps further by engineering a time travel movie that purposely keeps its viewer disoriented by the multiplicity and complexities that time travel would incur in the real world.

When two engineers working on an electromagnetic field that theoretically could reduce an object’s weight accidentally discover a method of time travel, they build two boxes that would allow them to travel back in time. Initially using this technology to play the stock market, and then to fix personal dilemmas that occur, both men eventually become rivals, with one wanting to further use the box for his personal gain and the other attempting to stop the experiment from ever occurring.

Shane Carruth–who wrote, directed, produced, and starred in Primer, his first film–created a cult sci-fi hit that has been noted for its complex structure and experimental narrative. Using time travel as a narrative device itself, Primer is a film that never fully explains itself to the audience, which has left many viewers discussing its ultimate structure and meaning since its release.

4. Inception (2010)

One of the most critically acclaimed and popular sci-fi films of all time is also one that has perplexed audiences since its release–which has only heightened its popularity. Following the enigmatic business of thief Cobb (Leonardo DiCaprio), who specializes in corporate espionage by entering the subconscious of his targets using experimental technology to steal secrets, from its outset Inception has a complex structure.

This only deepens as the audience watches Cobb and his crew exploring and explaining the mechanics of the dream world, which allows for the world to fold onto itself and impossible Escher-like constructions to occur. When they dive into the layers of a target’s subconscious to plant an idea but find themselves battle a security team–and Cobb his own personal demons–in this surreal environment, the audience is left wondering just what is real and whether they’re in reality by the end of the film.

Christopher Nolan is a master at complex narrative structures and playing sleight-of-hand tricks on the audience, and in this pursuit he’s never been more successful than with Inception.

Part of this comes from the nature of the realities Inception takes place in: largely taking place in the subconscious and other unreal spaces, there is such little time the film spends in “reality” that the audience can never quite tell if what they’re watching is actually happening–and largely it isn’t, even when it is. Its ambiguous closing scene only kept audiences arguing about whether or not Cobb is in reality–and one that hasn’t abated to this day.

3. The Adventures of Buckaroo Banzai Across The 8th Dimension (1984)

“What’s that watermelon doing there?” asks New Jersey (Jeff Goldblum) to Reno, both members of The Hong Kong Cavaliers, Buckaroo Banzai’s personal team of adventurers/rock stars, in the 1984 movie The Adventures of Buckaroo Banzai Across The 8th Dimension. It’s a good question but it’s ultimately irrelevant, especially since the first time you watch this movie you’ll have so many more questions as to what’s happening at any given moment.

Made in such a way that presupposes the audience would be well-familiar with the fictional, original, and first-time character Buckaroo Banzai (Peter Weller)–scientist, surgeon, rock star, and adventurer–this film starts with no exposition as to what’s going on and goes off from there. Purposefully constructed this way, W.D. Richter’s The Adventures of… bewildered audiences upon release but has since become a cult classic.

The first time you watch it, you’ll either find it enthralling that you haven’t been provided any reference point as to who these characters are and what’s going on or you will turn it off in frustration. By the third or fourth re-watch, after you finally put this puzzle of a movie together, you’ll understand what’s going on and appreciate this totally unique sci-fi action comedy–except for why the watermelon’s there. That’s one thing the film never explains. A full article about this film is available here on this website, under solid Cult Classic.

2. Solaris (1972)

Andrei Tarkovsky was one of Russia’s greatest directors, with many of his films–which centered on metaphysical and philosophical investigations of meaning, long unbroken takes, and unconventional dramatic structures that relied as much on character’s memories and dreams as much on the “actual” plot–often listed as some of the best ever made.

His entry into the sci-fi canon was bound to be complex, and with 1972’s Solaris, Tarkovsky made one of the most influential and enigmatic sci-fi films of all time. While the film takes place on a space station that’s orbiting the (fictional) planet of Solaris, the story mostly relies on the thoughts and emotional states of the scientists onboard studying the planet below. Centered around a psychologist who has been sent to the station to check on the emotional state of the astronauts, who have been sending confusing and disturbing messages back to Earth.

Upon arrival, he finds the crew behaving bizarrely and that a friend of his stationed on the Solaris station has committed suicide. The cause of the crew’s behavior becomes clear once the psychologist meets his late wife on-board, who is by all accounts real, but disturbed by this he sends her out on a space capsule…only she returns once again. Finding that these sorts of beings, whom the crew call “visitors,” have been the source of the crew’s upset since they take the form of people in their memories, the psychologist begins to work out what exactly these creatures are and why they’re appearing.

Memory, dreams, and the nature of life and love are not themes Western audiences expected to find in a sci-fi film in 1972, but Tarkovsky elevated the genre with Solaris into something more far-reaching and mysterious. Solaris doesn’t provide easy answers to the questions and situations it raises, but exploring the questions becomes a satisfying journey in itself when watching this film.

1. 2001: A Space Odyssey (1968)

One of the most influential sci-fi films ever made, Stanley Kubrick’s masterpiece 2001: A Space Odyssey can often come across as wilfully obscure to viewers. Starting at the dawn of man before cutting to 2001, where mankind is now travelling into space, before ending with a dazzling 20-minute wordless denouement that replicates the psychological, psychedelic experience an astronaut has after making contact with a mysterious alien artefact, the total effect of 2001: A Space Odyssey can floor first-time viewers with its massive scope and difficult-to-discern meaning.

Adapted from Arthur C. Clarke’s eponymous novel, the film–particularly its ending–makes more sense if one has read the novel, but Kubrick also freely adapted and interpreted the source material as he pleased. The visual effects of the film notwithstanding, which represented a massive leap forward in that field and setting a new standard for future sci-fi films to live up to, Kubrick added his signature open-to-interpretation touch to the movie.

The end of the film–in which an astronaut is pulled into a colorful vortex, which leads him to experience surreal events that include witnessing himself as an old man until reappearing in orbit around Earth as a newborn child wrapped in an orb of light–has left audiences scratching their heads as to its meaning for nearly 50 years.

This article was originally published on Taste of Cinema on September 21, 2017.