The Chicago Public Library
Perhaps the banner is misleading -- The Chicago Public Library isn't open 24 hours -- its web site is! Another example of how libraries are seeing their web sites as being as much the library as their physical building.

This is inside the main lobby. The railing circles an opening to the floor below, and above it is a domed ceiling. It was nearly closing time when I was there, so I didn't get much of a look around.