She

A professor is entreated by a dying colleague to take custody of the colleague's five-year old son, raise him to adulthood, and at that time pass on a chest to him. The professor does so, and when the child reaches adulthood and the chest is revealed, it leads them on an adventure to Africa. There they encounter a young queen of a lost race who says she's over two thousand years old, with an equally startling claim about the young man.
H. Rider Haggard invented the "lost world" genre of fiction with King Solomon's Mines, and he continued the theme, adding in a bit of romance, in She. Haggard wrote the book in six months "in a white heat, " and handed the manuscript to his agent with the remark, "There is what I shall be remembered by". Haggard was right : with its setting in darkest Africa and a woman at its center described as the most beautiful in the world, She was a sensation at its release, has never been out of print, and has sold upwards of 100 million copies.