The Barry Octagon at the National Gallery, London.
<a href="//www.flickr.com/people/42384834@N07" class="extiw" title="flickruser:42384834@N07">David Noah</a>
CC BY 2.0
<a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a>: <a rel="nofollow" class="external text" href="https://www.flickr.com/photos/42384834@N07/7375704728">The National Gallery</a>