Israel
I discovered I was Jewish when I was 15.
Prior to then, I knew that all my grandparents except my step-grandmother were Jewish, but I did not know enough about Judaism to know that Judaism was inherited. I thought it was more like Christianity, where you had to do something or believe something to be Christian.
That year, I took a comparitive religion course titled, "Religion: It's Nature and Practice". Our primary text book was The Religions of Man, with secondary sources including Night and Day by Elie Wiesel, Siddhartha by Hermann Hesse and several others.
In order to discover a bit about what being Jewish meant, I decided to travel to Israel and learn about it. I found out about the Alexander Muss High School in Israel program, and spent the 3rd quarter of my senior year in Israel.