I discovered invisibility while tripping once with a friend, in Georgia, when I was in the Army. No, really, I shit you not, but let me explain.

We popped some LSD (purple micro) and we sat against the wall of this building which was on the edge of Barton Field at Fort Gordon. There was a path going by where we were, but no one walking by ever looked our direction. It was just the layout of the trees and the clouds and the nearby buildings, they'd just naturally draw peoples' eyes along certain paths, and it so happened that they tended to draw peoples' attention AWAY from us. We were effectively invisible, yet sitting in plain sight tripping our balls off, laughing, occasionally waving our arms to see if even that would attract anyone's notice (it didn't).

It occurred to me that there are probably spots like that all over, if one only took the time to find them, spots where one can sit in plain sight, but because of the architecture and surroundings, no one will see you because no one will ever even look in your direction. I spent most of the rest of my time in the Army looking for such spots, and found them to be uncommon, but not incredibly rare. I found a couple of inviso-spots in Grenada, one in Turkey, and one so far in my hometown in the States, and I'm always looking for more because it is massively enjoyable to trip balls right in front of the world, yet remain totally unseen.