I was 10 years old.

My mother and I walked the dog to the Parade Ground, an annex of Prospect Park, Brooklyn, NY. We let the dog off the leash in the NW baseball field, and proceeded to muse the sky.
To our left, I saw what first looked like a submarine in the sky, not a whole lot higher than six storeys. I asked my mother if she was seeing what I was seeing.
We watched this huge dark grey cylinder, as close as grey can be to black, float silently over us, proceeding west.
I saw it close enough to emphatically state that if there was any semblance of  markings, or the fusilage beneath a blimp-type airship, I would have seen it. There were no windows, gondola beneath, no sound whatsoever.
When the length of it finally passed, I got up and ran to see the back and other side of it. At the back, there was an aperture - memory dosen't serve whether it was an arch or square or circular. But the other side of the cylinder's length was as unremarkable.
I arrived at at least 1200 feet in length from looking at maps of Brooklyn. In its entirety, the cylinder from my point of view stretched from Buckinham Road to Stratford Road - 1200 feet.
My mother and I compared our obsevation many times over the years. She says she saw a bulge in the center, thus in her eyes a cigar-shaped ufo. I saw a perfect cylinder, with a round nose and tail, the aperature issue kind of fuzzy to be sure enough to report upon.
The only time I felt apprehension was when I saw the opening at the end of the cylinder. I thought I might be discovered seeing something I wasn't meant to see.
The one thing we agree on is the hardest to describe. We both saw a dark, dark grey cylinder. We saw dark, looking at the side that floated past us, yet something told us there was light behind it, as if backlit. When I peered at the aperature, it was stone black.
It is years later, and thanks to the internet, I searched for accounts of cylinder sightings, and it brought me here.
Date is approximate.  PD