Don't be scared by the fact that it is a book. It is very accessible since it is divided into little articles on different areas of math. A lay person can read it and gain a sense of what this math stuff is and how varied it is. A PhD can read the same material and will appreciate it on a much deeper level.
Let me give one data point. I know more mathematicians who became interested in math because of reading The Mathematical Experience than any other book. Seriously.