This observatory was built by Christopher Wren in 1675 for John Flamsteed, the royal astronomer of Charles II (1660-85). It was then used by successive royal astronomers until 1948 when they moved to the less polluted skies of Sussex.

Today it is a museum, housing a wonderful display of historical astrological instruments including quadrants, sextants and telescopes. It is also worth noting that the octagonal room is one of only a few surviving interiors that were designed by Wren.

And of course this is where you can find the Greenwich Meridian Line. This is the Prime Meridian - the line that divides the globe into East and West and from which the world’s time is set. Greenwich Mean Time (GMT) is the term used for the current time at this line, and clocks and watches all the world over are set in relation to this.

The line also marks zero degrees longitude which offers a great photo opportunity - for you can get a picture of yourself with one foot in the Western Hemisphere and one in the Eastern Hemisphere.

Since 1833 a red time-ball on the north-eastern turret has climbed the mast at 12.58pm, dropping at 1pm precisely. This is so that the boats on the River Thames can accurately set their clocks each day.

Next to the observatory is the Greenwich Planetarium, which has a show every 30 minutes throughout the day.

The Old Royal Observatory is open from 10am-6pm Mondays to Saturdays and from noon-6pm Sundays. The admission fee is around ??????ut this includes entry to the National Maritime Museum and the Queen’s House as well.