This has always been a favourite of mine. When at school in Nairobi, Kenya, a group of us (mostly the band Members) were taken to a concert given by Louis Armstrong at the Nairobi Football Stadium. This was long before What A Wonderful World came out .. probably about 1959. So I was very lucky to see Louis Armstrong perform 'live'. I remember it was a very hot evening, and at one point Louis Armstrong took out his very white handkerchief, wiped his forehead and said, "'Scuse me. Me makeup's coming off!"
One of the comments under the YouTube video says:
His smile is amazing. When I'm feeling down this song never fails to turn me around what a wonderful day.
Hugh