As I remember, in about 3 years ago on a day of early summer with blue sky no cloud no wind, time at around 1300 – 1400 (can’t remember the exact hour), me and my neighbor having a chat in our terrace, I try to look up and enjoy the blue sky, (because in Belgium is rare to have blue sky), I saw an object with complete orange color (no shadow nor reflection) with perfect circle shape, stop at about 5-6 floors higher above my apartment with no sound, size about half size of a hot balloon, I asked my neighbor if she know what it is, but she said she don’t know. At that moment I told myself, “well maybe it’s a balloon”, then we continue our chatting, after a short while about a minute I looked up again, it’s gone can’t find it in the near area.
The strange this is, if there’s no wind and if it is not mechanic object, how can it fly away with no machine noise?

That’s my experience.

P.S.: If I see it again next time, I’ll think in mind to ask them to land.