A Choose Your Own Adventure classic! I couldn't call this site a school book fair if I did not have any CYOA now could I? 
 
This is a modern reprint of the old classic that is finally back in print after a 25-year wait!
 
You are hiking in Snake Canyon when you find yourself lost in the strange, dimly lit Cave of Time. And depending on which of the curving paths you take, you’ll emerge into a different thrilling moment in history. Will you be adopted into a band of early humans and hunt down a woolly mammoth? 40 possible endings!! 
 
Don't forget to pick up a few bookmarks to "keep your place" as you decide what to do next!