Black object at least 20,000 ft. up, over a highly restricted air zone in a military base, most likely undetected by radar.I walked outside to check out a thunderstorm that was brewing near my house, I thought that maybe it was going to become severe like one thunderstorm that came by a few days ago. When I looked at the edge of the thundercloud, I saw a completely black object at least 20,000 ft. up in the atmosphere. The object was so high up that I couldn't make out any details, only could I make out very general details. The object moved slowly and smoothly and no engine sound was emitted, of course it was so high up. Although the object was to small to be an airliner, and it was way of course the usual plane route. My house happens to be under a MAJOR plane route and every single day at least 150 planes fly above my house, so I'm quite familiar with planes because I see them so often. I strongly believe that the object WASN'T a bird, because I really doubt they fly so high up, we do have a lot of birds in Puerto Rico anyways! Well before I could get someone to see it for th! emselves or a camera at least, the object dissappeared behind a cloud. What interests me is that the flying object was flying over a highly restricted air zone, here in Ft. Buchanan, only military helicopters and commercial airliners are allowed to fly over the base. I'd really like that government officials have a better eye out on the sky around here, who knows if the object was a threat? If it was human, it could have dropped a bomb, don't you agree? But I highly doubt it was human anyway, it was moving in a way so smooth, that no other plane I've seen has ever flown so gracefully.