This shot is from the 2002 show ‘Gene(sis),’ courtesy henry art gallery

At the top of the wood stairs at Western Bridge, there's a photograph of an icehouse by Catherine Opie. The icehouse, smack in the middle of the photograph, is barely visible—resting between snow-covered land and snow-colored sky. This photograph appeared here a few weeks ago. When I look at the icehouse, I also see, in my mind's eye, the interior of a Vermont apartment, drawn life-size in sumi ink on rough paper by Dawn Clements, and a patch of Amazon jungle at night, photographed with the least possible light by which you could make a photograph, by Solange Fabião, because those are the works that were hanging in this spot, on this wall, before the icehouse appeared. All three works—the one up now, and the memory of the other two—are part of the same show, referred to by the gallery as Title variable. The exhibition has been changing constantly, and quietly, since October. When one work is swapped out for another, a press release is sent out and a new exhibition title is announced, but there is no new opening. There is no wiping clean of the white walls and starting over. Title variable has a past—its own—built into it.

The truth is, there are ghostly alternative exhibitions everywhere, waiting to be recognized. Even empty walls aren't blank: Every wall has its history, and what you've seen there before never really goes away. Last year, the artist Michael Asher built a temporary installation at the Santa Monica Museum of Art re-creating all the stud walls that had been built in 10 years of exhibitions there. If you close your eyes, you might be able to do something similar at your favorite gallery. Over time, you build your own shows. Most of us don't own art, we just remember it.

Some walls are so prominent (the wall facing the top of the first escalator at the Seattle Art Museum) or so unusual (the cylindrical light-well at the Henry Art Gallery) that they're blatantly mnemonic. But inspired by Western Bridge's show, I wanted to test the theory that even mousy walls unleash a torrent of images. So I selected a mousy wall on the lowest level of the Henry Art Gallery. It is referred to by the people who work at the museum as the north wall of the Stroum (or south) Gallery. For the rest of us: Go down the stairs all the way, enter the main gallery, and this wall is on your right.

What comes to mind first—among all the things I've seen on this wall—is a temple made of human hair, approximately the height of a small real church (52 feet tall, some research reminds me). It hugged the wall. The hair formed letters that looked like Chinese and Arabic and Hindi and Roman. But the supposedly English words didn't exist—so you suspected, but couldn't be sure, that all the languages were fake. It was called Temple of Heaven, by the artist Wenda Gu. Even in heaven, nothing will be understood, I thought at the time, which seemed reassuring, and still does.

Temple of Heaven was in the show Inside Out: New Chinese Art in 1999, the year I moved to the Northwest. The things I've seen on the wall since then have included a throbbingly colorful group of photographs of sluglike trails of DNA samples by Inigo Manglano-Ovalle (such precise portraits that were yet so ungiving) and Andy Warhol's advertising drawings from the 1950s. Is anything more innocent and simple and free than Warhol's early drawings? They are portraits, too. He especially liked to draw shoes, in side view—pointy-toed shoes with straps and ties in saturated colors. I can't help but picture those bright shoes walking around on this wall, leaving the DNA trails that would appear later.

At the very top of this particular wall at the Henry is a skinny window overlooking the museum's outdoor courtyard. On this window once appeared a famous statement by Bruce Nauman written in spiraling aquamarine neon letters between red neon lines: "The true artist helps the world by revealing mystic truths." Soon after, I recall, post–Vietnam War artist Kim Jones made drawings directly on this wall, in pencil, flying like weather patterns between a tricycle and a wagon. Jones makes "war" drawings, meaning that they represent a battle between two sides that he has been drawing since he was a child. There are the occasional tactical advantages, but overall, no one is winning, which means they can continue fighting.

I can imagine Jones in front of that wall, working with his pencil for hours, standing beneath the window where Nauman's message was, and right in the place where U-shaped white neon tubes measuring Nauman's body had hung, sticking out of the wall like tuning forks. The tubes would have hugged Jones as he worked if they'd still been there. A few years earlier, in this spot, Jones would have been facing a tribe of enormous anime girls with red eyes, figures of post-nuclear Japan. (The exhibition: Superflat. The work: Chiho Aoshima's 50-foot nightmarish mural.) Or zombie-ish, gibberish-talking Eastern Europeans sitting in unmoving cars inside a haunted old Communist-era concrete pavilion. (In: a video by Croatian artist David Maljkovic.)

This one wall—if you've been looking at it long enough, and are fairly good at remembering what you've seen—offers a surprisingly coherent imaginary exhibition. It is an exhibition having something to do with zombies and gibberish and war and religion and science and art and shoes. Not a bad summation of the last half of the 20th century and the start of the 21st. Right now this wall is painted black and there's no art on it at all, as if to say, "What wall?" recommended