Lilith

... my spectral face shall come between his eyes
and the soft face of her, my name shall rise,
unutter'd, in each thought that goes to her;
and in the quiet waters of her gaze
shall lurk a siren-lure that beckons him
down halls of death and sinful chambers dim:
he shall not know her nor her gentle ways
nor rest, content, by her sufficing source,
but, under stress of the veil'd stars, shall force
her simple bloom to perilous delight

Thus speaks Lilith in the Poems of the Australian poet Christopher Brennan. The realm of innocence in Brennan's poem is represented by Eve, but Lilith stands for the realm of experience: the wisdom given by the snake. It's an old and oft-repeated argument, from some of the ancient gnostics all the way up to Philip Pullmann's His Dark Materials trilogy: we are torn between innocence and experience, purity and danger. Innocence is beautiful in children, and losing it feels somehow like Original Sin, like a fall "down halls of death and sinful chambers dim". But we are not supposed to remain in the garden, beyond good and evil: we are supposed to learn to know ourselves. Essentially this means the confrontation with eros and sexuality, with the realm that Christianity has so tragically come to confuse with sin (the American scholar of religion Jeff Kripal has written a fascinating book on this, The Serpent's Gift).
And what about beauty in this context? Tastes differ, but for me, the Pre-Rafaelites have been supreme in exploring the erotic boundary between innocence and experience: their female nudes are not only among the most beautiful one will find anywhere, but these women have real faces: no matter how beautiful one may find Botticelli's Venus or the nymphs of the Primavera, these are no real persons who have lived and suffered. Like Eve perhaps, you might admire them as abstract ideals, but you cannot make love to them and they will never make love to you.