Expo67
Still one of the most amazing places I've ever been. The multimedia presentations and 'futureness' of the whole experience was awesome. I was into Buckminster Fuller at the time, so seeing the U.S. pavilion (see post card) was stunning.

One of the highlights for me was in the French exhibit. They had a huge laser with an invisible beam that was close to an inch across unfocused. You could see this as the presenter passed a piece of wood through the beam and it instantly burned. The focused beam would burn through a firebrick in a couple dozen seconds.

I had been very interesting in lasers by this time, so I recall seeing the demo a couple of times. After one one, I got up the nerve to ask the presenter to burn something for me-this postcard of the American Exhibition. He flicked the card quickly in the focused beam to leave the roughly parabolic burn. (There is a bit of 30 year old masking tape holding it together.)