Beneath the Swedish capital lies an intricate web of underground train lines. More than 90 of the 100 stations in the 110km tunnel system, sometimes referred to as “the world’s longest art gallery”, have been decorated with paintings, installations, mosaics and sculptures by 150 artists since the 1950s. After spending a couple of weeks exploring arctic Norway and Sweden, London-based travel photographer Conor MacNeill headed underground to capture images of the metro stations. Here: A rainbow arcs over a girl on the platform of Stadion station. (Photo by Conor MacNeill/The Observer)

Chris Staring photographs a mysterious train graveyard in the heart of southern Bolivia, where the skeletons of British steam locomotives and rail cars rust away on the edge of the world’s largest salt flats. More than 100 rail cars and locomotives can be found in different states of decay in the train graveyard. (Photo by Chris Staring/Rex Features/Shutterstock)

After the success of their Superman series in 2013, the Canadian Mint debuted a new set of coins honouring the Man of Steel at this year's Fan Expo in Toronto. The collection is made up of three silver coins worth $10, $15 and $20, and a gold coin worth $100. Photo: Close-up of the $10 silver coin in the new Superman series from the Royal Canadian Mint. (Photo by The Canadian Press)

In this handout from the Ministry of Defence, Royal Air Force VC10 and Tristar air-to-air refuelling aircraft support the first UK air combat mission in support of UN Resolution 1973 in flight on March 19, 2011. Col Muammar Gaddafi has vowed a “long war” against the “crusader aggression” after over 100 missiles were fired by the US and UK, during multi-national action aimed at enforcing a UN-mandated no-fly zone. (Photo by SAC Neil Chapman/MoD via Getty Images)

In this artist illustration handout from the National Aeronautics and Space Administration (NASA), the Upper Atmosphere Research Satellite (UARS) is seen. According to NASA, the 12,500 pound satellite will fall from orbit into earth's atmosphere anytime between September 22 through 24. It is estimated that the space craft will break up into about 100 pieces, with an estimated 26 of which could hit the earth over a possible 500 mile debris field. (Illustration by NASA via Getty Images)

People wait in beds during the The World's Biggest Breakfast in Bed Guinness World Record Attempt at Martin Place on March 2, 2012 in Sydney, Australia. 289 Australians join forces to create history as Martin Place is transformed into a giant bedroom. All participants was enjoy a substantial breakfast served in bed by celebrity chef “Fast” Ed Halmagyi and a free goodie bag valued at over $100. (Photo by Ryan Pierse/Getty Images)

Carlos Martinez (L), a representative of the Guinness World Records, examines the cooking process of a chocolate coin during an attempt to break the Guinness World Record for the biggest chocolate coin in Caracas, Venezuela, October 1, 2015. More than 80 people will work with 100% Venezuelan cacao to create the coin that is estimated to weigh 1,000 kg, according to local media. (Photo by Carlos Garcia Rawlins/Reuters)

Women wearing "Shiroshozoku" or the traditional white robe pray as they bathe in ice-cold water at the Teppozu Inari shrine in Tokyo, Japan, January 10, 2016. About 100 participants took part in the Shinto ceremony to purify their souls and wish for good health in the new year. (Photo by Yuya Shino/Reuters)