Dark rectangle, almost a cube; no lights, no sound, no wings, no reflective surface, seen in daylightIt was 7:30AM, sunny, no clouds. I looked up because the sun glinted off an airplane very very high in the sky. Below it I noticed a very dark, but not totally black, object moving southwest slowly in a straight line. It looked small - because of the altitude, I suppose, though I had no context to determine its true size or altitude. Holding my arm straight out and up I'd say it appeared 1/4 the size of the nail on my little finger. It was a dark rectangle, almost a cube. It appeared to tumble slowly once in a while because sometimes I could catch a glimpse of blue sky as if it were not just a cube, but a very thick U shape. Hm, that sounds weird. Maybe it would be better to say that the solid shape had a bite out of the edge and I could see the blue sky through it when it presented that face to me. It did not reflect light, it had no wings, there were no lights on it, and I couldn't hear it. There was no trail. It was high off the horizon and traversed maybe 50 degrees; it was never near the horizon. When I first noticed it, it was maybe over Lake Forest Park or Lake Washington. I was looking north. I watched it until it got to a bit south of NE 104th St where I was standing on 15th Ave NE, but farther west. Then it appeared to stop, though it could have been going due west and only appeared to stop since I was looking west by then. Then after 15 seconds or so, it very slowly, slower than it had gone southwest, started going north, though it may have only looked like it was going so slow if it were actually going northwest. It was slowly getting smaller. At that point the bus came and I stopped watching. I thought it might be a weather balloon (not that I've ever seen one) but the shape was not round and unless there were upper altitude winds blowing straight southwest, the line of travel didn't seem consistent with a balloon drifting around. That's my story and I'm sticking to it. P.S. I am not a UFO enthusiast.