It took a trip to the military prison at Guantanamo Bay to get me to notice gates C-19 and B-32 at Logan International Airport.

Having lived through the nightmare in New York City of that day, I knew as well as anyone that the two planes that destroyed the towers had taken off from Boston.

Gates C-19 and B-32, where flights 11 and 175 departed, are still in active daily operation: there’s a good chance you may have walked through one yourself in the last 20 years without realizing. As you wait for your plane and walk through the entrance ramp, there’s nothing at all to let you know that you’re retracing the steps of the terrorists and some of their victims.

The only markers are outside. An American flag sits atop the end of each gate. The flags are on short poles, and easy to miss. It’s almost impossible to notice that they are the only gates in the airport with this understated decoration.

Logan International Airport features as a key thruway on the extensive evidence trail developed by the military commissions trying the five men accused of plotting the 9/11 attacks. At a 2017 hearing, I heard FBI witnesses testify that lead hijacker Mohammed Atta’s checked bag didn’t make his flight. We saw photos of the luggage, and the tags and other documents with those gate numbers on them.

I’ve never visited the 9/11 memorial at Logan, but since that hearing, every time I’m there, I try to get a glimpse of either gate. It’s almost ritualistic, having to lay eyes on them, like one might try to locate an out-of-the-way shrine.

I was working for WNYC, New York’s local NPR, on the day of the attacks. We got knocked out of our offices, just blocks away from the twin towers, for a couple of weeks. Returning to the office meant daily walks past the pile of rubble that burned for months.

Some wanted to re-build the towers exactly as they were, just 10 feet taller, a show of strength or defiance. The first time that I saw the flag on the C-19 gate, I was a little angry. It felt weak and forgettable, nondescript. If you weren’t looking for it, you surely wouldn’t see it — we see flags all over the place. But I can’t judge the airlines or the port authority; I don’t have any better idea of what to do.

When I go to lower Manhattan now, even though it’s somewhere I lived and worked for so long, I don’t recognize it. I find trips back to Ground Zero unnerving. It’s not precisely reassuring that Logan’s gates are unchanged, but it offers something, at least, kept frozen in time to recall that day.

In the wake of the attacks, it quickly came out that all 19 terrorists were brown men, and as a brown man, for a moment, I was scared of being targeted. Just as quickly, I realized there was no place I’d rather be than New York City at that moment. There were vigils, strangers would hug and cry together. My white neighbors in Brooklyn would go out of their way to make eye contact and smile at me. We weren’t just okay, we were better, stronger, unified.

Going to the prison at Guantanamo Bay has shown me just the opposite. I’ve been to the base close to 10 times over the last decade. I’ve seen Khalid Shaikh Mohammed, the ‘mastermind’ who came up the plan to hijack planes with boxcutters and fly them into buildings, and had briefer glimpses of the hundreds of others being held who were never charged with any crime. We learned in some detail about the abuse of the 9/11 defendants, the waterboarding and worse. We learned that one of the defendants sat on a pillow because of the damage he’d suffered from brutal sexual abuse at the hands of the CIA.

There’s no doubt that Khalid Shaikh Mohammed and his crew were evil. But what I came to feel, deep in my bones, on those trips to “Camp Justice,” was how successful the attacks had been. They had brought out evil in us. And it was there in front of me in brick and stone and barbed wire, next to a beautiful beach in the Caribbean.

We started out with unity, and it breaks my heart that this is what remains: a forever prison, and a forever war. And two lonely flags at Logan.