Space in living room

is that a fireplace? Get a great, as in size and looks, painting or print over it. Or a collection of photos/prints/artwork all in the same style and color of frames. You’ve got enough wall there to do 7 or 9 pictures. A vase or urn with great faux grass or seed pods in the corner.

You could do a mantle-type shelf, but it really looks too low for that to be attractive and sensible.

Not seeing the other end of the room, can you install wall to wall shelves over the fireplace, like a mantle??

I see a beautiful Gallery wall of prints, mirrors, shelves, wreath. an accent table the possibilities are endless. I started this collection with the two hydrangea prints that I believe I picked up at Home Goods, the plate shelves are from IKEA, very inexpensive. The eagle is the first wall decor for my first apartment in 1973 - when eagles were the rage...I couldn't part with it, so I painted it cream and made it work! Good luck! Have fun!

A built-in with storage underneath would look amazing, filled with books and knick-knacks and provide storage.

I don't know what the black area is...but in THAT corner I see one of those tall, skinny 'corn plants'..probably not the right name but you see them in many office. Take very little light. A tall plant for sure & it will give you oxygen & eat any CO2.....big win.

I would paint the niche a metallic blue or like an ocean.... https://www.youtube.com/watch?v=O5KNo00WVZk

https://www.amazon.com/Rust-Oleum-253537-Metallic-Accents-Paint/dp/B003EELN0K/ref=sr_1_1?ie=UTF8&qid=1523930795&sr=8-1&keywords=rustoleum%2Bmetallic%2Bpaint%2Bquart&th=1

or use a ocean tapestry and apply it with liquid starch to the whole nice area.... https://www.twinkledeals.com/ocean-tapestry/deals/

then outline the aquarium with LED strip lights to make it really stand out.... https://www.amazon.com/s/ref=nb_sb_ss_c_1_6?url=search-alias%3Daps&field-keywords=led+strip+lights&sprefix=LED+st%2Caps%2C237&crid=73TQSN1TOKAD

Looks like a natural place to hang photos or artwork. A clock hung on the wall with a table below that would work too. A small stereo would fit in their also. Or you could just put in shelves and make it look like built in shelving.

Oops. Well, shoot. Get yourself an old buffet, paint it if you like, and put your tv on it. They have lots of closed storage and always look good. I love practical furnishings - especially storage. It’s yard sale season and lots of us old folk are downsizing furniture made out of real wood.