PPG Skywalk over Fourth Avenue, Pittsburgh. Note: I snapped this "illegal" photo just minutes before security instructed me that photos of the building are not allowed.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/53969873@N00">Michael Righi</a> from Pittsburgh, USA
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/michaelrighi/18955628/">PPG Skywalk</a>