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)

Stunning silhouettes under European cities reveal the size and splendor of the continent’s urban foundations. Photographer and content-manager Anna Arinova, 28, from Moscow, captured the awe-inspiring labyrinths in Russia and Germany. Here: Regenwurmlager, Poland. The Regenwurmlager is an extensive underground fortification area constructed by Germany in 1920s-1940s, now in western Poland, near the city of Międzyrzecz. (Photo by Anna Arinova/Caters News)

Belly dancer Nagwa Fouad sailing on the river Nile, 1972. Egypt is one of 23 countries represented at the Dubai Photo Exhibition, showing off photography that dates to the 1920s. Dubai Photo Exhibition is in various venues of Dubai’s design district from 16-19 March. (Photo by Farouk Ibrahim)

Everton fan and legendary fashion photographer Matt Lever has captured the dizzying drama behind the scenes at catwalk shows since 1999. Here: Balmain, Spring/Summer 2011. (Photo by Matt Lever)

These stunning images show the beauty and drama of Mother Nature at work. Captured deep in heart of the Danakil Desert in East Africa, the images show the acid pools near the Erta Ale volcano. Pools of brightly colored acid can be seen amid the dramatic blast of volcanic ash. The photos were taken by Neta Dekel, an Israeli photographer. He the acid pools were one of the most extraordinary sights he had ever seen. (Photo by Neta Dekel/Caters News Agency)

“These incredible shots show the stunning formations of an iceberg beneath the surface of the ocean. Taken in Tasiilaq, Greenland, by Franco Banfi, the underwater photography captures the beauty of these ice mountains beneath the ocean’s surface. In some of the photos, divers are swimming around an iceberg under the frozen water, while other images show some of the weird and wonderful creatures you can encounter in that part of the ocean”. (Photo by Franco Banfi/Caters News Agency)

A leopard attacks an Indian man as others climb a wall to get away from the animal in Lamba Pind area in Jalandhar on January 31, 2019. After a leopard was spotted in a house in Lamba Pind area of Jalandhar city, subsequent attempts to capture it led to the animal attacking at least six people, though none was injured seriously, local media said. (Photo by Shammi Mehra/AFP Photo)

A loved-up couple have captured the moments they shared a dip-kiss in different locations around the world. Rob, 34, and Joli Switzer, 33, from Maryland, embark on a minimum of four international holidays per year to ensure that they get their unique dip-kiss photograph. Here: Rob Switzer 34 proposed to Joli 33 whilst they were on holiday in Moscow, Russia. (Photo by Dipkiss Travels/Caters News Agency)