You can use cushions, pillows and a throw blanket and have a little reading area or if you're not into reading you can decorate it with a few accessories and pictures on the wall.

I was going to suggest a reading nook too (since there is a light above). Maybe get a custom made cushion, or alternatively just a bunch of pillows and throws.

I agree that adding a cushion and pillows would make for an adorable reading nook. If that's not your style it could be You could also add some storage if you add some corner shelving.

A custom shaped two inch thick pillow and a couple of throw pillows on top for a seating area.

Would help to see the whole wall, but I'd lean toward something like a medium-sized floor lamp that fits your style (removing the one from overhead), and/or a striking vase or set of baskets.

It should be noted that this "awkward ledge" was almost certainly designed as a convenient place to put your TV where it would be near the fireplace and still down at a reasonable viewing height, so another, um, solution would be to put the TV there and put some nice art over your fireplace instead.

Perhaps a large plant that will really fill up the space and provide color and texture.

Try a basket of fuel for the fire. But first tackle the TV and high-water curtain issues. Remove the frail looking light; the stones are overpowering it.

I think it was intended for firewood, so I’d stack some even if I had a gas insert.

I agree w/deco. do something w/the tv, wires, cables and box.

if you don't want a cushion,

Or, put a few potted plants there. done.

I would have the corner leveled using a cement material. Then I would have either a stone slab or a 2”-thick stained-and-sealed wood counter/table top made to fit there. Bring the TV down from the mantel, place it on the new surface and hide that tangle of wires.

I would put a basket of cozy blankets there.

Start by putting the TV anywhere else. The screen should be at SEATED EYE LEVEL (or slightly lower - if furniture placement allows). Relate corner cushions/ throws to fabrics already in the room.

I would remove the celling light fixture. Then, I would soften the space by adding a plant (4-5 foot tree). There are also fabric covered floor lamps that are tall and provide soft diffused light. These are stand alone lamps. I have one in a corner in my dining room and I think it fills the awkward space well.