On the fourth floor of Seattle Art Museum, there is a corner room that has a history as an escape hatch, a secret doorway. This is the spot where a few years ago the museum displayed the charged instruments of a sacred soul-quest ceremony practiced by the people native to the land beneath the museum. Entering now, you're given a pair of glasses that, once you put them up to your eyes, begin to show you tantalizing things that don't look right, views that are pornographically heightened compared to the flat paintings in the other galleries. It is dizzying. The pain kicks in, right between the eyes, at the same time as the fascination.

Without the glasses, what you see are rows of black-and-white prints that look like postcards on the walls, each postcard with a pair of images that picture the same thing but that are slightly different. But with stereoscopic glasses, each picture is presented to a single eye, and then the brain—using its natural capacity to combine the two views of your two eyes into a united vision—layers them to present you with a single scene that appears three-dimensional.

The stereoscope is a form of entertainment invented in 1838, and it became so popular in the 19th century that it was considered dangerous. It was, indeed, the perfect delivery system for porn, and here, it turns the level surfaces of landscape photographs into zones where even the air is swollen. The moment the brain registers the effect—it takes a second of looking, where the strain comes in—objects in the foreground pop up, suddenly erect. But despite the illusion of realism, the views aren't correct—they don't look the way it would actually look if you stood on the frozen ground in front of a man standing deep inside a glacier (one of the many in-credible views at SAM).

It's the exaggerations, the perversions, that make stereoscopes fundamentally different from photography and cinema—and that make stereoscopes signs of a historic remapping of ideas about truth, looking, and the way human bodies work in the world, writes art historian Jonathan Crary. Around the time the stereoscope was developed, writers on science also became preoccupied with the idiosyncrasies of human vision—the exceptions that disproved old rules of objective seeing—especially the afterimages that appear when you close your eyes and an image recurs, then fades, changing color and shape as it goes. An afterimage is your own possession. It doesn't belong to the world, but to the mind. The variations of subjectivity became the new normal, along with the sense that, as Crary wrote, "perception was not instantaneous." It takes time to register a stereoscopic image, and you can only hold it for so long. What's more, the image you're seeing is not the one that's hanging on the wall—the image you're seeing does not exist outside your brain.

Artists always say they want their works to be completed by their viewers, for the artistic process to be a form of live, mutual communication. Stereoscopic images don't exist without their viewers. They are visual information as a form of messy, embodied, titillating, pain-inducing—unstable—exchange. The opposite of, say, money. Crary draws an eyebrow-raising parallel between photography and money—both of which he sets in opposition to the experiential nature of stereoscopes. Photography and money, he writes, "are magical forms that establish a new set of abstract relations between individuals and things and impose those relations as the real." Meanwhile, stereoscopes are unreal, in every great sense of the word, a reminder of the essentially unhinged nature of the way we see.

Another dizzying room—a room physically tilted on its axis—is now to be found a few miles south. It is called, ominously, Demon Hill. It's an artwork by Los Angeles–based Julian Hoeber, who built it out of plywood, and it stands inside the gallery at Western Bridge. It's based on the "mystery spots" that became popular American roadside attractions in the second half of the 20th century—Demon Hill is based on the specific location in the redwoods at Santa Cruz, where, according to lore, a stretch of earth is tilted off-kilter in a reality-bending geographical anomaly.

The artwork is part of a show of three distinct environments at Western Bridge, all falling under the title Funhouse. One is a bounce house by Mungo Thomson—you do jump inside it—that references the transcendent Skyspaces of American Light & Space artist (and Quaker) James Turrell. The other is a circular enclosure by Carsten Höller where white neon lights flicker on and off in patterns, appearing to travel the circle and create a hallucinatory architecture that's continually changing. These pieces have been seen before at Western Bridge, but this is the first showing for Demon Hill, which Hoeber created for the Hammer Museum in Los Angeles in 2010.

To enter Demon Hill, you walk up a small ramp into the single room, decorated only with a mirror, a shelf, a metal plumb on a string, and a chair, lit by rows of fluorescent lights above. The chair is based on a plain design by minimalist artist Donald Judd; the lights above reference light artist Dan Flavin. But art historical references really only exist outside the room. When you're inside, your consciousness is entirely occupied with attempting to make sense of what's going on—and failing. "What Magritte's Perfidy of Images is to the cerebrum, the mystery spot is to the cerebellum," wrote William Poundstone after seeing Demon Hill. (The Perfidy famously reads, "This is not a pipe" with a painting of a pipe.) "But this paradox plays for keeps—there is no explaining anything to the cerebellum." Instead of clicking into clarity, the experience is of perpetual vertigo.

Because the room is tilted, what looks level is, in fact, way off the center of the earth's gravity. That means that inside Demon Hill, there is the distinct sensation that you could reel off the surface of the earth into senseless orbit. You simply cannot reconcile what you see with what you feel. There's a fight going on: Either your eyes are lying or the rest of your body is. And you can't stop trying to make reconciliation happen, to achieve sensory unity.

A series of tricks—what essayist Luc Sante calls "meditative chicanery"—gives you something to do with all this tension. The plumb dangles at such an obscenely severe angle to your line of sight that you have to laugh. A break! The artist has provided a ping-pong ball for you to roll along the length of the shelf; because of the room's angle, the ball appears to roll upward. Holding out the promise of rest, the chair is like the horizon line in a landscape painting. When you finally get over to it and sit down, though, you mainly just feel dizzy in a new and different way.

Dizziness is your signal, as with the stereoscopes, that truth is just truthiness, as Stephen Colbert would put it. It's a simple and familiar idea, but still one that could set you free or drive you crazy. Poor Nietzsche, writing in the era of the stereoscope and seeing—and fearing—its chaotic power: "Reason is the road to the constant," he insisted, like a robot trying to argue with a human. "The least sensual ideas must be the closest to the true world. It is from the senses that most misfortunes come—they are deceivers, deluders, destroyers." But who'd want to live without them?