When you see a St John Ambulance it’s hard to imagine you are looking at nearly 1,000 years of extraordinary history. In 1080 a hospital was started in Jerusalem by monks to tend for the pilgrims. During the crusades they also took on a military role. Their history is long and sometimes very violent. The Priory in Clerkenwell which became their headquarters is definitely worth visiting.
http://museumstjohn.org.uk/ 8 minutes Barbican tube