At 4:15 p.m. I was driving westbound on Belleview Avenue and noticed an object in the sky. It was very stark against the clear, blue sky and that's what made me notice it. When I first saw it, it seemed quite far away, but drifted east toward where I was. At first, I thought it was a helicopter monitoring rush-hour traffic, but it's movements were not like a helicopter and when I got a better look at it as it came closer, it was obvious it was not a helicopter. It was disc-shaped, but somewhat morphic - it seemed to alternate in shape and it seemed to be drifting with and/or coasting on the wind and it was very fluid in its movements and covered some distance very quickly. It was approximately 1/2 to 3/4 of a mile away when I got a fairly good look at it. It was difficult to keep my eye on it, however, as I was driving and went under the I-25/Belleview bridge. It was traveling in a SSW direction and as I continued on Belleview, I pulled off the avenue (street/junction just before Monaco & Belleview, adjacent to office park). It didn't look like anything I'd seen before, and I know this will sound weird, but its movements reminded me of a dance ... its movements were just very fluid and graceful. But it was NOT a bird! That I know for certain! I thought maybe it could be a balloon of some sort, but its outer shell was definitely metallic, but not shiny, like mylar or polished silver ... it was more like a gun-metal gray, muted but finished enough to catch the sun's reflection. It rose and fell in altitude as it continued SSW, changing color from the sun's reflection (I think), then continued to rise in altitude before I lost sight of it. It was a clear afternoon, no clouds, but a slight, smoggy haze, and the afternoon sun was very bright.