Shiny saucer shaped vehicle over downtown Seattle displayed various speeds and altitude accelerations.At approximately 15:45 I saw something shiny in the corner of my eye as I was eating lunch on the 18th floor of a downtown building. I was looking south toward Safeco Field when I realized that what I was seeing was NOT a plane. It looked like a tin can in the wind, except it looked in control and it varied in speed. Also, it hovered like a helicopter at times. It was black on top and very shiny (almost like a mirror) on the bottom. At first I thought it might be the stealth fighter, but I don't remember the stealth being able to manuever quite like this vehicle. Once it got to West Seattle, it shot up straight (from approx. 5,000 ft. to at least 35,000). I couldn't believe what I was seeing. It was NOT a plane, nor the stealth, nor some weather balloon. This thing then zigzagged and must have flipped backwards. It then shot up again, probably another 5-10,000 ft. I could see it's black speck hovering for about 10 minutes. Then it just followed the cloud format! ions back towards downtown Seattle heading east, very slow.I'm a student at the UW and a runner who doesn't take drugs or make stuff up. In fact, I'd say I'm a good citizen who strives to better not only my life but the lives of others as well. What I saw was incredible and exiting, but very unexplainable and a bit scary too.