The Cenotaph - Whitehall, London, UK - Satellite Imagery Oddities on Waymarking.com

The Royal British Legion website tells us:

A cenotaph - which literally means Empty Tomb in Greek - is a tomb or monument erected to honour a person or group of persons whose remains are elsewhere.

Standing in Whitehall is probably the best-known cenotaph in the modern world. It was designed by Sir Edwin Lutyens and constructed from Portland stone. It is undecorated save for a carved wreath on each end and the words "The Glorious Dead".

The sides of the Cenotaph are not parallel, but if extended would meet at a point some 1 mile (1.6 km) above the ground. Similarly, the "horizontal" surfaces are in fact sections of a sphere whose centre would be 900 feet (270 m) below ground.

It is flanked on each side by various flags of the United Kingdom. The flags displayed since 2007 represent the Royal Navy, the British Army, the Royal Air Force, and the Merchant Navy.

Uniformed service personnel (excluding fire and ambulance personnel) always salute the Cenotaph as they pass. The Cenotaph is the site of the annual National Service of Remembrance held at 11.00am on Remembrance Sunday, the second Sunday in November.

The English Heritage website tells us about the project to clean the Cenotaph in 2013:

The iconic and internationally recognised Whitehall Cenotaph in London's Whitehall which will be the focus of the commemorations on Remembrance Sunday and Armistice Day, was cleaned and repaired this summer by English Heritage in preparation for this weekend's Remembrance Sunday and the First World War centenary commemorations of the next four years. The highly skilled conservation works began at the end of April and were completed in July. The Cenotaph's Portland stone is naturally susceptible to weathering and pollution and although English Heritage carries out maintenance every year, a more thorough cleaning was needed. The Cenotaph is listed at Grade I and is widely regarded as one of the most iconic and poignant war memorials in the world.

 The famous British architect Sir Edwin Lutyens (1869-1944) produced his design for the Cenotaph within hours of the Peace Treaty marking the formal end of the First World War being signed on 28 June 1919. Intended only as a temporary part of the celebrations which followed, the Cenotaph was originally made of wood and plaster. However, the public reaction to the monument was so strong - the monument was soon piled high with flowers - that Lutyens was commissioned to design a permanent memorial.

Derived from the Greek, Cenotaph means 'empty tomb' - a monument erected in honour of a person or group of people whose remains are elsewhere. One of the most renowned memorials anywhere in the world, the Whitehall Cenotaph honours the more than 1.1million British and Commonwealth soldiers who died in the First World War.

Drawing inspiration from classical architecture, Lutyens designed a Cenotaph whose power lies in its apparent simplicity, typified in the brevity of its inscription: The Glorious Dead. However, the design is more complex than is at first obvious. There are no straight lines.  Instead every surface is subtly curved with the raking verticals meeting at an imaginary point 1,000ft above the ground, designed to bridge the space between Heaven and Earth.

The Cenotaph was unveiled by King George V as he made his way to the ceremony for the Unknown Warrior in Westminster Abbey on 11 November 1920. It quickly became the nation's focal point when expressing grief and gratitude for the sacrifices of the First World War, and also for the conflicts which followed. It was estimated that within five days more than a million people had filed past, laying 100,000 wreaths. The monument had taken its place in the nation's heart as a poignant marker of remembrance.