The old Passimeter has a good exhibition about underground architecture and Charles Holden
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/87347455@N00">Chris Sampson</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/lodekka/4837090727/">ARNOS GROVE-05 240710 CPS</a>