Nothing. The mirror is the star of that space. The ledge adds a geometrical accent, complete with shadows. If you raise the mirror several inches, you may be able to put something on there, but it will detract from the mirror and the ledge.

I agree nothing should be on the ledge

Nada

Zilch. Zero. Zip.

^^^^

Less is more! I also agree nothing.

Having nothing would look fine, but I know that I would HAVE to put something there....way too tempting. Keep it empty sometimes or put a snowman there when the time comes :)

Thought about this for a while and since you have this need to fill the ledge.....what about tea lights.

It would look wonderful lit when you have company over.

I thought pf tea lights too. I would do an entire row...like 9 or so..I would jut do the simple small glass ones...cool and inexpensive ;)

I love the pink orchid in Groveraxle’s mock up.

A single narrow wooden box less than a foot long and centered on the shelf … as if put there to hide keys or notes passed between family members … would be interesting.

and/or

You might consider either painting an accent stripe (color different from wall color) or adding wallpaper trim tape to ONLY the vertical side of the curved space and let it serve as an underline for the mirror w/o decoration

(except, perhaps, small holiday decorations: pumpkins in fall; changed to holiday decoration in December; changed to snowman in January; changed to red heart shaped knickknack(s) in February; changed to green and/or shamrock decoration in March; then tiny basket; then something red/white/blue, etc.) .

Nothing or what groveraxle said!

Thank you everyone!

Nothing and no bench

The shape of the bench fights the niche and the mirror I would not have a bench there.

I placed a bench there so company can sit down to put their shoes on

The bench a tally looks bigger in the picture than it really is

Nothing, but paint the “ledge” white as the woodwork. As Beverly suggests, a white something under.

TOV Furniture Oppland Bench, White · More Info

In an effort to be useful, I've implemented some of the above suggestions:

I couldn't find a row of tealights, so I just installed some Christmas candles:

Love the candles!

Does this qualify as a "geometric" ornament you were thinking of?