Wow, I am so enjoying the wonderful stories in this thread!
Tracing my father's mother's family and building a tree from scratch was amazing because we knew almost nothing about her.
Suspecting, and then proving, that my 4th-great-grandfather (on my mother's side) was Jewish was pretty amazing, since that knowledge had not been passed down to us by my mother's grandmother (and she had to have known, since she had Jewish aunts, uncles and cousins).
Regards,
Josephine