Jejudo, South Korea
You're playing with some pretty traditional images here and taking them in different directions. I like that, but you might want to make the rhythm a bit more traditional emphasize that contrast. Another contrast might be my own recent poem where I was trying to do something quite different in a new form. Most of the complaints, here and at other sites, deal with how far away I get from the form itself. I think that kind of straining is necessary but you can go too far.
Here's a quick summary of the first line:
She STANDS at the WINDOW of her CAStle of GLASS,
--Why 'the' if the whole castle is glass?
--The 'of' repetition bothers me here, it strains the power of repetition. The 'window in the middle also strains the rhythm. It slows down that first anapest, 'at the win' but 'dow of her' messes with the whole rhythm. I find I can't read it as anything but a dactyl, 'DOW of her' which trips me up because I want to hear that 'dow' in relation to window and not that foot. Naturally, I want to stress that first 'of' but that isn't what I do when I read it out loud.
--If any of that makes sense, I think you've got to make this one more iambic from the very start.
--Enough rhythm talk, I'll try to address other points in the rest:
And views the wonders of the meadows so sweet.
--so sweet seems artificial to me.
She, a young and beautiful lass.
In a glass castle she can't be discreet.
--I don't see the relationship here except in terms of the rhyme. It's explained later, I suppose, but don't forget rhyme works with you're meaning/syntax, it doesn't create it.
Her Knight now peers through her walls of glass.
--Capital on knight? 'Her knight' is an interesting use of possessiveness given the rest of the poem. I think you can expand this image though, give the knight more eagerness perhaps.
Yet neither does she care to hide.
--With hide here, you have a great rhyming verb for what you want to say side, ride, bide, abide, guide, tried, etc. I think you're missing an opportunity in not exploring that.
For wither he comes or wither he goes,
He will always remain outside.
He trusted and loved her with all of his heart,
Yet she with another was smitten.
Breaking his heart and scorching his soul,
As he read the cold letter she'd written.
--Why not give us the letter and use a different form. Since the knight is the one being hurt, let's get more of the feeling he feels. Let's react the way he reacts.
Now all alone in her castle of glass,
Exposed to the world is she.
--Try to avoid this kind of inversion. I suppose it's okay given the archaism you're using but it still struck me as off.
Waiting perhaps for a brave night to come,
--I like the play on night/knight. Uh, do you read Marvel comics? Know anything about Death (not Brad Pitt, but a beautiful woman who is loved by the evil Thanos) -- be great if you kept working on that and it would also explain why she is in a castle of glass, her love for another 'night', and her disdain for the knight. Just an idea,
And rescue her, setting her free
--I've said a lot here and can't touch on everything but, honestly, I think this has a lot of potential, I like the reversals between the knight and the 'lass', and I like the ambiguity at the end. Definitely a lot you can do with this one.