Add either a large mirror which adds interest and also gives the illusion of space, or do either a tapestry, because it will soften the space naturally, or a collection of photos or art pieces because a single piece will be overwhelmingly big, or feel dwarfed. Also if you'd rather not do a hanging of any kind, investing in unique lights or plants would be a fun and fresh alternative.

It looks like you have little kids. How about making a collage of their artwork which can rotate as they get older? You can mix in family photos too. Either that or moss wall. :)

I would make it a gallery wall. Large items and medium size items.

I cannot see what the décor is in the room below, so don't have a clue about colors or styles. I would suggest a large painting and that's all. If you are not sure about a picture gallery, then don't do it. A large piece of art will fill the wall and create interest. Don't clutter it up with a bunch of stuff.

If you want to post your accent colors I can do some shopping for you.

A lower hanging light fixture is a great start. It will bring the eye down to a more normal level & away from the vent & recessed lights in the ceiling. (Paint the vent the same color as the wall color. It will make it visually disappear.)

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A nice potted plant can also be added to the right of the light.

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Try pulling the sofa away from the wall so it can be centered in front of the fireplace.

This picture is 50 x 50" might look nice on the wall.

the wall art installations are great solution when you need to fit the size of art to your space. We create hand blown glass wall art ready to hang. Please feel free to contact us for custom project for your wall.

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These range from 60 X 48 to 48 X 48, which I think is the smallest I would go. Check for more here: http://www.houzz.com/projects/1295077/art-original-abstract-paintings

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A large piece of Art can really bring in a wave of deftness to your room. It acts as a style to your room.

Here's some suggestion below......to know more about my Art work and collections please visit my shop on Etsy website -

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Some suggestions below - many more available.