The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21 as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, located 62 feet below the surface of the Atlantic Ocean in the Florida Keys National Marine Sanctuary. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. During simulated spacewalks carried out underwater, they will evaluate tools and mission operation techniques that could be used in future space missions, including journeys to Mars. (Photo by Karl Shreeves/NASA)

“The Berlin Wall (German: Berliner Mauer) was a barrier constructed by the German Democratic Republic (GDR, East Germany) starting on 13 August 1961, that completely cut off West Berlin from surrounding East Germany and from East Berlin. The barrier included guard towers placed along large concrete walls, which circumscribed a wide area (later known as the “death strip”) that contained anti-vehicle trenches, “fakir beds” and other defenses. The Soviet-dominated Eastern Bloc officially claimed that the wall was erected to protect its population from fascist elements conspiring to prevent the “will of the people” in building a socialist state in East Germany. However, in practice, the Wall served to prevent the massive emigration and defection that marked Germany and the communist Eastern Bloc during the post-World War II period”. – Wikipedia

Photo: West Berlin policemen and East German Volkspolizei face each other across the border in Berlin, circa 1955. (Photo by Three Lions/Hulton Archive/Getty Images)

In this Thursday, May 8, 2014 photo, Iranian coal miners push metal carts to be loaded with coal at a mine near the city of Zirab 212 kilometers (132 miles) northeast of the capital Tehran, on a mountain in Mazandaran province, Iran. International sanctions linked to the decade-long dispute over Iran's nuclear program have hindered the import of heavy machinery and modern technology in all sectors, and coal mining is no exception. (Photo by Ebrahim Noroozi/AP Photo)

In this October 7, 2014, photo, Fredrick Brower, center, helps cut up a bowhead whale caught by Inupiat subsistence hunters on a field near Barrow, Alaska. Drawing on tradition, and keeping within the closely monitored Aboriginal subsistence whaling guidelines, a bowhead whale is carved and divided by a crew armed with knives and hooks, and then shared according to custom. (Photo by Gregory Bull/AP Photo)

Baldwin Street, in Dunedin, New Zealand, is considered the world's steepest residential street. It is located in the residential suburb of North East Valley, 3.5 kilometres (2.2 mi) northeast of Dunedin's city centre.

Revelers celebrate during fireworks marking the start of the New Year on Copacabana beach on January 1, 2017 in Rio de Janeiro, Brazil. (Photo by Mario Tama/Getty Images)