What makes a watch the most valuable in the world? It’s supercomplicated – literally. In 1925 banker Henry Graves Jr. (considered the greatest watch collector of the 20th century) commissioned Patek Philippe to create a unique gold pocket watch. When Graves finally received it – eight years later – it was the most complex timepiece ever created by human hands... (Photo by Suzanne Plunkett/Reuters)

Bulgarian Roma women from the close-knit Kalaidjii clan attend a so-called “bride fair” in a suburb of the city of Plovdiv April 13, 2015. Each year Roma families from the close-knit Kalaidjii clan gather during what they call a “bride fair”, an event offering parents a chance to meet and to arrange marriages for their children. (Photo by Stoyan Nenov/Reuters)

“Dover Castle is a medieval castle in the town of the same name in the English county of Kent. It was founded in the 12th century and has been described as the “Key to England” due to its defensive significance throughout history. It is the largest castle in England.

The outbreak of the Second World War in 1939 saw the tunnels converted first into an air-raid shelter and then later into a military command centre and underground hospital. In May 1940, Admiral Sir Bertram Ramsey directed the evacuation of French and British soldiers from Dunkirk, code-named Operation Dynamo, from his headquarters in the cliff tunnels”. – Wikipedia

Photo: The Repeater Station in the subterranean tunnels underneath Dover Castle, which has been restored by English Heritage for a public exhibition on June 3, 2011 in Dover, England. The evacuation of allied soldiers from Dunkirk was masterminded and co-ordinated from the secret command and control centre in the tunnels deep below the castle. (Photo by Matthew Lloyd/Getty Images)

Hundreds of houses painted in bright colors in what organizers claim is Mexico's largest mural, is part of a government-sponsored project is called Pachuca Paints Itself, in the Palmitas neighborhood, in Pachuca, Mexico, Thursday, July 30, 2015. German Crew is the artist collective responsible for painting the mural project. Director Enrique Gomez, who goes by MYBE, said the crew has painted 1,500 square meters with 20,000 liters of paint. Working hand-in-hand with residents, muralists have painted the facades of 200 homes bright lavender, lime green, incandescent orange – hues more commonly found in a bag of Skittles than in the drab, cement-and-cinderblock neighborhoods where many of Mexico's poor live. The project aims to bring the community together and rehabilitate the area. (Photo by Sofia Jaramillo/AP Photo)

An incredible view of Thunderstorms light up the insides of clouds near a beautiful sky line. This is truly heavenly weather as pictures taken from an airplane cockpit reveal what pilots see from above. It looks like at cruising altitude the weather really hots up, with the flight deck revealing some amazing scenes. Thunderstorms light up the insides of clouds, lightening streaks across the sky like cracks in a windscreen, the northern lights sweep uninterrupted across the sky and the galaxy stretches on forever. The pictures were captured by senior first officer Christiaan van Heijst, a 33-year-old from the Netherlands, and his friend Daan Krans. (Photo by Christiaan van Heijst/Daan Krans/Caters News Agency)

Camel herders scoop up water in plastic buckets from one of the few watering holes in the area, to water their animals near the drought-affected village of Bandarero, near Moyale town on the Ethiopian border, in northern Kenya, Friday, March 3, 2017. The U.N. humanitarian chief, Stephen O'Brien, toured Bandarero village on Friday and called on the international community to act to “avert the very worst of the effects of drought and to avert a famine to make sure we don't go from what is deep suffering to a catastrophe”. (Photo by Ben Curtis/AP Photo)