Martin Gardner has just recently passed away. I remember really liking his books when I was in high school, but I haven’t looked at them since then.
One of his essays convinced me back in high school that trying to visualize the fourth dimension was dangerous. Charles Hinton invented a system of cubes to teach you to visualize the fourth dimension. Gardner printed a letter (copies at banubula and waggish) from someone who said that the cubes were bad for your mental health. It wasn’t until sometime after taking linear algebra that the feeling dissipated.
More on the cubes can be found at The Fairyland of Geometry.