London - Old Royal Observatory

Must-see attractions nearby: St Paul's Cathedral Tower of London Trafalgar Square Westminster Abbey British Museum Victoria & Albert Museum Greenwich

Four of the rooms are furnished in the style of the 17th century. On a mast topping one of the towers of the house is a red time ball which drops from the top of the pole at 1 pm precisely every day - a device originally intended to enable vessels in the river to regulate their chronometers.

The zero meridian of longitude, dividing the globe into eastern and western halves, runs through the Meridian Building. The point is marked by a steel rod in the floor. The building also houses an interesting exhibition of old astronomical instruments.

The Equatorial Building is dominated by the dome housing the largest telescope in Britain. Public demonstrations of the telescope take place every afternoon.

The Royal Observatory has undergone some extensive renovations, to build a new planetarium and astronomy galleries.