This morning I participated in the third annual Twin Cities Memory Walk. I walked with my company’s corporate team—and also in honor of my grandma Iris, who died of Alzheimer’s disease several years ago.

All told, it was a wonderful Saturday morning. But ironically, on the way to the walk, I had an experience that gave me a sliver of insight into what it might be like to live with this disease.

The walkers were asked to park in a ramp about a mile and a half from the starting line. The entrance was very well marked, so I had no trouble getting into the ramp or catching the shuttle bus.

The shuttle bus made a right turn from the parking area onto Bush Lake Road, and started up a long hill. I recognized it as the same hill that had caused my high-school bus driver so much aggravation every time it snowed. (On one particularly wintry afternoon, he called for volunteers to lie under the tires, for traction.)

Then, I saw the entrance to a wooded trail I used to walk at least twice a week. In my youth, it was a single narrow footpath on which I routinely encountered poison ivy, red foxes, possums, and swarms of bees (sometimes—to my dismay—all at once). Now it’s broad and paved, with a striped yellow line down the middle.

The shuttle passed Highwood Drive. I wouldn’t have recognized it, except for the street sign. What used to be a narrow road winding into the woods is now a suburban-style four-lane street, with ornate retaining walls that welcome visitors. It bore no resemblance to the desolate road I used to navigate on my skateboard.

The shuttle continued west, past Bush Lake, where my sisters used to swim in the summer. (As the keeper of the family swimming pool, I hated them for this. Almost invariably, they would ride their bikes home from the lake and immediately jump in the pool to cool off. I was always fighting off some algae infestation or other in that damned pool.)

But I digress.

What struck me about this little trip down memory lane was that the memories from my past were so vivid—as if they’d happened just yesterday—but they bore little resemblance to what I was seeing outside that shuttle bus window.

I wondered if that’s how it was for my Grandma Iris in those last years of her life: Everything seeming at once so familiar, yet also so alien and so new.

I don’t know whether Alzheimer’s disease is among the ailments I’ve yet to inherit. But today’s events served as a reminder of how incredibly frail our memories are—and how precious.