I noticed some security warnings when opening https://tools.wmflabs.org/monumental/ For example:
Loading mixed (insecure) display content “http://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Haarlem%20-%20Bakenessergracht%2055.JPG&width=120” on a secure page[Learn More] bundle.min.js:17:8818
Loading mixed (insecure) display content “http://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Bakenesserkerk%20haarlem.jpg&width=120” on a secure page[Learn More] bundle.min.js:17:8818
Loading mixed (insecure) display content “http://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Haarlem%20bank%20van%20lening.jpg&width=120” on a secure page[Learn More] bundle.min.js:17:8818
Loading mixed (insecure) display content “http://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Exterieur%20AULA%20-%20Haarlem%20-%2020284746%20-%20RCE.jpg&width=120” on a secure page[Learn More] bundle.min.js:17:8818

Probably best to just load all Commons contents using https