Why not a couple of great designer chairs and wall unit to display a collection of books and art pieces and an awesome lamp for reading if you ever want to get away from everyone. A couple of these chairs and something like the second pic for display.

You could go with a billiards table if your not looking for formal and want to have fun!

Paint the walls white to give more light. The light coming through the window is north, south, east or west?. With white walls, make the space into a gallery, one side pictures and the facing side photographs. Change them once a month? In the centre have an S shaped chair (lovers seat?) with two small coffee tables with art and photography books under them. Pale plane carpet which you already have would make a space for thing, gazing and even daydreaming. How about that? Good luck

It can be a game room, a library, or a music room.....find a function and how you would like to use the room than we can design the space accordingly.

Library/reading nook with shelves along that wall to the left and a comfy chair/ottoman with a reading lamp and side table for your favorite hot drink. Maybe a colorful throw to stay snug when reading and napping while dreaming about all those wonderful places you read about. (photos from the web, chosen because they appear to have large windows like your space)

You could also do a cool home office like this one:

Rainy day window seat/bed with pillows, books on two walls, and a nice chair like this: http://www.pinterest.com/pin/260927372132768683/

Hello,

Here are a few things you could add to brighten the room and make it seem less empty.

1. Add a built-in window bench under the window.

2. Add mirrors or a large painting to the left wall

3. On either side of the wall on the window you could put hanging flower vases or candle holders.

4. Add a rug to create more depth and brighten the room.

Best Wishes,
Architecture Studios

How about an office or study?

I like the previous idea of a gallery, but my favorite would be a library wall with ladder and at least two chairs for reading with a small table and good lamp; a round pedestal table in the center, piled with books, would be so welcoming I think, and perhaps a place for kids to read, play games, etc. Lots of ideas in the comments, so just think about how you live and how your family might utilize this wonderful, light extra space! Best of success.

I LOVE the idea of a yoga studio! You could also do a bar room!

Wow, such great ideas. Thank you all very much!

By the way, how would a built in window seat accommodate for the two vents in the floor? There must be a way to redirect?

I've seen people move the two vents forward so they are still in the floor, just moved in front of the window seat. I've also seen window seats where they brought the vents out of the front of the bench. I think it depends on the design of the bench and who you have doing the work. In general, if you have hardwood floors, moving them might be more of a problem because of creating a hole in the existing floor. But if you have carpet over a subfloor, then it is less of an issue. Here's a photo of how one person put their vent in the front.

This would make a great space for a library. Lots of shelves and built ins. Maybe you could use some of the built ins for storage space for extra dishes or anything we tend to accumulate.

This is a great space with some design challenges. If you entertain could be used as a dry bar with a beverage frige and a pub table or two. If you are into wine it could be a great space for a wine bar with a nice sampling table.

I think making it a library would be a great use for it, especially with the existence of that wide window. It will make for a great reading nook.

If there were shelving built ins on the left wall, how high would you suggest they go?

Thank you for your suggestions! I really love how it turned out, and just in time for a 4 year old princess party. Now, I just need furniture...

I love that you have posted a before and after photo :)

Looks fantastic! Love the pretty princess and the balloons in the photo :-)

That is totally awesome and such a great reading nook! Good light and comfy pillows. Now add the some of the right books to encourage princesses that reading is cool!

I'm so glad you followed up and showed us the finished project! I'd probably add a floor lamp in the right hand corner over a comfortable chair with ottoman and a small side table to place a hot drink on.

I’ve since added two wingback chairs w ottomans, and an end table between. Thank you again for your help. I adore the space so much more.

Next to the dining room? Make it a bar.