Our exuberant tour guide invited them up, a man and young girl, to stand on the level wooden platform. With each standing at either end, the guide had the pair hold a wooden board between them on their heads, showing us, the audience, a sloping angle down from his head to hers.

Then she asked them to switch sides, and hold the board between them again. The angle still sloped, but this time it was noticeably different. But neither father nor daughter changed height. They stood at the same places on the platform, used the same board between them. It was eerie, off-putting, and all of us just stared, dumbfounded into silence.

There was no way to explain it, and our tour guide offered little help. In lieu of an explanation, she just smiled, and let the mystery of the Oregon Vortex sink in.

Arguably one of Oregon's best-known roadside attractions, found between Grants Pass and Medford in southern Oregon, the Vortex first opened in 1930, and has been drawing tourists ever since to Gold Hill, in southern Oregon. The land was once a gold mining claim, they say, until a poorly-built cabin collapsed on one end. John Litster, a physicist and geologist, developed the property in the 1920s, conducting experiments on the land until his death in 1959.

Many of those experiments are what tour guides at the Vortex still show today - apparent changes in height, objects appearing to roll uphill, and an unseen force that in some places seems to pull you off balance.

Elena Cooper, the manager and tour guide who showed my group the Vortex, said they have no explanation for the phenomenon. Visitors tend to offer their own, from Biblical rapture to quantum leap, but the guides don't play favorites, armed instead with levels and boards, there just to show off the mystery.

"We say, 'this is what it looks like and here's the truth,'" Cooper said. "Why it does that, we don't know."

The closest thing the owners of the Oregon Vortex have to an explanation is this: Present on this land is a "whirlpool of force" that plays with your perspective. As you walk toward magnetic south, you appear to grow taller, as you go back toward magnetic north, you appear to get shorter.

At every demonstration of this effect, tour guides use levels to show that there's no funny business. Some contend that it's an illusion of angles, but photographic evidence can debunk that. Skeptical scientists often bring equipment to measure the effect, but Cooper said they all walk away just as confused as the rest of us.

The Oregon Vortex isn't shocking as much as it is intriguing, but its 87 years of continued popularity is proof that you need little else to run a successful roadside attraction.

"You actually have to have a truly magic thing that will make people want to come see it," Cooper said. "To our advantage, there really is a thing here."

After his death, Lister's wife sold the business to Ernie and Irene Cooper. Their daughter, Dody, took over in 1980 and still runs it today - though her son, Mark, and daughter-in-law, manager and tour guide Elena Cooper, are in the process of taking over the Vortex for the foreseeable future.

So while Oregon's other roadside attractions struggle with an uncertain future, the Oregon Vortex promises to stick around, offering up the mystery to skeptics and true believers for generations to come. Because at its heart is a universal appeal - an inexplicable phenomenon that's as humbling as it is entertaining.

"The idea that we understand the universe is the height of hubris," Cooper said.

So while you think you might know what the Oregon Vortex is or isn't, odds are, you have no idea. Nobody does. And figuring it out isn't really the point. It's more fun to just experience the strange attraction, smile and let the mystery of the Vortex sink in.

--Jamie Hale | jhale@oregonian.com | @HaleJamesB