Yoga room, nursery, panic room, more closet space?

Make it a woman cave;)

Library, office, craft room.

The best idea for these types of spaces are multi-functional. Some of the questions we might ask to figure out just what type of things you like to do and your family make-up. do you have small children. Or maybe older children that like to do art or need a good homework space. Maybe a space for the kids to hang out. Or if this isn't the case. Perhaps turning it into a partial library, and storage. Here's an idea.

I would use that as an office/exercise area. Maybe a built in around the window with a seat and storage like someone posted, then a nice desk and space for a yoga mat (although the fluffy carpet might be bad for yoga, so something else). Add some nice lighting with lamps and enjoy a room to get away from everything.

If you need storage or a nursery though, this is a perfect place for it.

Or how about a great dressing room? You could have a pull-down ironing board or steamer for wardrobe touchup. It would also be a great place for laundry facilities.

Dressing room for the lady of the house made as fancy as she likes what a luxury that would be

An exercise room with massage chair