How to dress up these windows and give the area life ...

window planters??? These are on my stairwell , my stairs are kinda spiral and open on both sides. So hanging a picture wouldn’t give balance . I want to put something in these windowsills to give life to that area but what ?? There are 3 of them... HELP
A better shot of windowsill,the sill is 4 “ wide by 21 “ long.
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