A design for Atlanta’s new concert hall, designed by Santiago Calatrava, has been unveiled. “The building, roughly as tall as 13 stories, features a ribbed-glass roof surrounded by a metal collar. A smaller version, which houses a recital hall and learning center, nestles on the south side. Each is adorned with a free-standing, ridged steel arch that is 186 feet (about 18 stories) at its highest point. The Spanish architect calls it the feather.”