Hi rock
I read all the von Daniken ("extra-terrestrials were here") books when they first came out, and enjoyed them tremendously. Okay I was a teenager then, and fairly gullible I suppose... but they make one think of what may have happened, and what's possible! Here's the author's website if you want to know more.
http://www.daniken.com/e/index.html
By the way, my very smart Dad (who passed away last year age 93) told me at the time -- "well, he [meaning von Daniken] may be full of hooey but he sure does tell a good story". So whether or not you are a believer, the books make for grand reading!