They are beautifully proportioned and trimmed windows. That being said, as you can see at night they become "black holes." So I think a simple window treatment would be a good choice. See below some ideas for you:

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Always loved curved or arched curtain rods. It's rare to find a set of arched windows like yours all same sized on one wall. This would look beautiful on yours. Surprisingly easy to buy too. Custom made is an option too. Amazon sells them as well.

I would do Roman shades like this:

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I love those windows as they are. Unless you feel the need for privacy at night--I know I would--I'd leave them alone. They really are beautiful!

I love them just as they are .

Diana, thank you, you hit the nail on the head in that they do become black holes at night! I really like the photos you posted, beautiful window treatments that fit my style. My dilemma is that all the photos I can find are like those where there is space for a pair flanking each window. I only have 20” between each window, making only enough space for a single panel and am not sure how that would look?

Houssaon, yes! Roman shades similar to your photo are what I had in mind as a possibility

Aphaea, thank you! I don’t need for privacy/sun, only to dress them up!

They add so much to your room. What about the other side? In the sun room hang panels just under the arches. I really think it looks forced when people don't just ignore the arch. That way you could lose the black holes at night and keep the beauty of those windows in your room. Otherwise go with one long rod with stacks to the far right and far left of the three. Rod goes just below the arch. Anything else would be just too too much.

I think 20” is plenty of room for a single panel. Rule of thumb is to have fabric 2.5-3 times the width of the space you’re covering (to give a nice full look). So if you’re thinking dummy panels, that’s 50-60 inches of fabric. Ready made curtains usually come 50” wide, so 20” is kind of perfect.

Here is a quick and not so great mock up. I really like the Moores Mill idea that Diana posted.

Another way not to have black holes at night is to install landscape lighting outside of the windows so you see illuminated plants/trees outside and not pitch black.

Because you don't need privacy, I'd hang a lacy curtain over just the rectangular part, leaving the arch bare. No drape, just the lace panel.

Aktillery9 that IS a great mock up, thank you so much. It gives me a much better vision of what curtains could look like on those windows!

I am glad it helps Cat. Sometimes you just need to see your own room with various options!

I would suggest that you hire a custom curtain fabricator for those windows. It is a pricey option, but the end result is so much better than if you tried to do it yourself with ready-made curtains. You'll not only get a great product but expert professional advice on the many details that come up. And they will last for a good long time.

Beautiful room. You could do a beatuiful sheer drpaery or romans below the arch. Also, Natural Woven shades could be pretty below the arch.

Yes, I am in the business of selling blinds and shades - actually minimalistic bottom-up top-down shades that can be an inside mount installation to very shallow spaces of only 1/2 inch. But in your case, do not do anything. The room is perfect as it is!!!

Update! Thank you to all who took the time to comment. I chose natural cordless Roman shades and custom drapery panels to frame but not cover up the windows. That along with a little furniture rearranging and it looks like a different room! Still working on the throw pillows but I am loving the space now.

You did a great job--fantastic room!!!

That is a very beautiful room! I have not been following, just picked up on your thread this evening, so elegant! Any way I could bother you to see your art beside your piano? Just if you can, i would much appreciate. Thank you in advance.

I am glad the curtain panels were hung so as not to hide the beautiful window casements.

@alice Edwards thank you! Here is a closer up of the painting. My husband and I met and lived in Philly for many years and bought this from a local artist before moving to NC. It’s a view from the top of the iconic philadelphia museum of art (Rocky Balboa) steps, looking down towards city hall, scenery we saw daily while living there, and the apartment we lived in was just off to the right. I love original and/or meaningful art in a home!

Painting

Thank you Cat, the colors of the art are just wow! Very nice piece. Actually spent a bit of time in Philly myself in my younger years living in Lehigh Valley PA. Thank you