Wow, niches galore! Perhaps you could create some sort of ensemble among the whatever is placed in the niche (e.g., painting, tapestry) and the objects placed on the two steps in front of it. Or maybe an ensemble that also includes the right-hand niche as its the height of the lower step and the shallow niche is the height of the upper step.

-- amateur

I'd put in shelving. Love when the space on the sides of a fireplace is utilized that way. Especially if you can balance it out on both sides.

firewood. or a single striking sculpture.

Go big or go home! The candlesticks approach the right scale, but are too utilitarian. All the items in the other shelf are too small to be appreciated, or even identified, from across the room. Here's the kind of scale I'm talking about.

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It looks like it is for firewood, and it would look great!

Real firewood

What style and color are your furnishings? Not a fan of wood in house.

I assumed contemporary look and went with white and black palette. I added black marble pieces to far display shelves to ground that area.

Firewood might work there. It looks like perhaps that was what it is there for. Notice the niche in the image below?

Alpine Ski Home · More Info

I had something similar in a former home. I got some fresh-cut river birch logs to stack. They were bug-free and didn’t decay a bit. We lived there 13 years. Now, the new owners are trying to sell it, and I looked at the pictures online. The same river birch logs are still there, unchanged.