One great idea we dug up from the internet is painting your own windows!
http://lemontreecreations.blogspot.com/2011/02/ballerina-big-girl-room.html
This project could take an INFINITE amount of directions....and has plenty of room for improvisation! Paint a few and put them in a bedroom, dining room, bathroom, pantry, or any other room to give it a nice open, spacial (or even illusion-like) feel!
Great for all ages, and don't forget canvas is still buy ONE get TWO FREE at CC Lowell (wink wink)!
The sky is the limit!