In "La Belle Dame Sans Merci," what attracts the knight to the lady?

It is clear that from the beginning enchantment or some
form of magic is at the heart of the attraction that the strange lady is able to provoke
in the Knight who is left the worse for ever meeting her. However, at the same time, it
is clear that the lady's beauty has something to do with it. Note the way that the
knight describes the lady in stanza four:

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I met a lady in the
meads,

Full beautiful--a faery's
child;

Her hair was long, her foot was
light,

And her eyes were
wild.

Note the way that her
beauty and her enchantment are linked in this stanza. She is "full beautiful," in fact
so beautiful that the knight concludes she was a "faery's child," or the product of
magic. The "wild" description of her eyes combined with the way that she made "sweet
moan" also add a frankly sexual element to the attraction. The way she is described and
the actions that she engages in suggests that she is casting some kind of spell over the
night, as she sings a "faery's song" to him and gives him "roots of relish sweet" and
other such offerings to eat. Reference to her "wild, wild eyes" is again made later on
in the poem when the knight kisses her eyes four times and closes
them.

Thus it is that if we examine the poem the nature of
the attraction seems to be in the way that the lady is able to enchant the knight with
her beauty and magic. Her other-wordly nature is stressed throughout the poem, and so we
can imagine that the knight finds her exotic and attractive.