Agreed - don’t put anything there.

That appears to be an architect opps. The vault extends past the doorway. What a mess. Be glad its in a room no one but you goes into. Leave it empty, fill it with a vase it doesn't matter no one but you will ever see it!

I suggest leaving it empty. Extending the closet wall up to the ceiling will create an odd transition at the ceiling so that’s not a good option.

Don't decorate it then it will fade away.

Will you post a wide shot of the room? The trim around your closet (or door) is unusual for a bedroom, what type of molding and trim is in the rest of the room?
I think the detailed trim unnecessarily draws the eye to the awkward spot but without seeing the rest of the room it's hard to say.

The ultimate solution would be to extend the wall to the ceiling.

We had the same in all the bedrooms in our previous home, we just ignored them, no decor, didn’t want to draw attention to them.

No decor. It’s worth pricing the cost to dry wall it up. That is a dust collector, for sure.

Agree with nothing.

Not every space needs to be decorated.

A wider view can certainly help…it looks like a possible storage space …used for seasonal items only needed once a year..perhaps🤷🏻‍♀️

But if you have more storage than you need …I agree just cover it up…still ….posting a better view can do no harm…

Sometimes varying the color of the difference angles can make the angles more interesting …and intentional….

I think it's architectural thing to just leave it but nothing or some kind of lighting up there that is nice nothing needs to be done

Going Goldblum is always the way:

Maybe now they’ll ignore the niche. ;)

Nice to see you, Jilly!✨

Thank you, you too!

Yes, I’d ignore it. :)