"The land, through which we have gone to spy it out, is a land that devours its inhabitants, and all the people that we saw in it are of great height. And there we saw the Nephilim (the sons of Anak, who come from the Nephilim), and we seemed to ourselves like grasshoppers, and so we seemed to them." (Numbers 13:32-33, English Standard Version)
Check out the Wikipedia too.
Have you thought of reading the Book of Enoch? I have often wondered if, over the aeons since their falling, the Nephilim might have changed their initial appearance and habits. Anyone any thoughts about that possibility?