Share 'Things in science that made you go "wow!"'

There are quite a few things in scientific studies that really made me go "wow!", and completely transformed the way I saw my surroundings, and I thought that a discussion where everyone could mention what made them go "wow!" would be a nice way of discovering new and fascinating scientific tidbits.   I'm in biology, and I think the biggest amazement I've had was when I discovered the existence o…