Bird’s Nest Stadium, designed for the Beijing Olympics, looks pretty incredible - as do many of the other buildings created for the Olympics. But for every building that gets built, there are many ideas that don’t. For the national stadium, China had a competition. Here are some of the other entries (click on thumbnails to see a larger picture): 
“a symbolic link - a bridge - between old and new,” apparently, the roof moves as 2 leaves, but I dont really understand how…
“a floating water lily surrounded by petals and blossoms,” the central roof can open to a perimeter of 130 meters
yep, another retractable roof, complete with UFO aesthetics
pretty neat shape that doesnt show in the thumbnail. click on image to see larger picture
I don’t understand this, but apparently the floating thing is a suspending retractable roof
See the 13 finalist entries, multiple pictures of each and a full explanation here.
