There were crowds of tourists on the hill where the Royal Observatory, Greenwich is situated. The views over London are stunning and the area is very interesting. The Greenwich Meridian runs through the site. This is a line of longitude that was selected in 1884 by an international conference to be the common zero of longitude and the standard for time reckoning throughout the world - hence Greenwich Mean Time or GMT. A red ball (which you can just see in the top and bottom photos) still drops at precisely 1pm every day. The observatory was commissioned in 1675 by Charles I (to carry out work to assist the navigation of ships) but today the buildings are kept as a museum and the scientific work goes on elsewhere.