Christopher Wren designed the Greenwich Royal Observatory in 1675. Two centuries later the Prime Meridian of the world, 0° of longitude, was established there. Besides its historical interest, the site is a leader in bringing astronomy to the public, in part through the Peter Harrison Planetarium.
Here is the courtyard of the old Royal Observatory in Greenwich. A strip is set into the paving to mark the meridian line. Some visitors are having their picture taken standing on it and in front of the meridian monument. A number of people prefer to have their pictures taken straddling the line, so they can say they have a foot in each hemisphere!