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)

Michael O’Neill won a prize in animal portraits with fry of a peacock bass hovering around their mother for protection against predators in South Florida. (Photo by Michael Patrick O'Neill/2016 National Geographic Nature Photographer of the Year)

“This grey adult male seal enjoys a good grin while lying on the beach”. (Photo by Michael Hutch/SplashdownDirect via Rex USA)

Private Harold L. Langhofer edges into the ball-turret, March 9, 1943. Curled in this position, he can turn the turret so that it fires in any direction. The turret can also be swung around so that the hatch opens into the plane, and the gunner can crawl into it while the Flying Fortress is in motion. (Photo by AP Photo)

Television actress Catherine Fuller visits Trafalgar Square in London and feeds the famous pigeons. (Photo by Harry Kerr/BIPs/Getty Images). 26th June 1956

Australian actress Joy Smithers poses beside a poster featuring Australian cricketer Brett Lee during the official launch of the AceStar underwear range at Pink Salt on August 19, 2008 in Sydney, Australia. (Photo by Mike Flokis/Getty Images)

The sun shines on trees that are displaying their autumn colours surrounding Palladian bridge and the lakeside Pantheon at the National Trust's Stourhead on November 3, 2010 near Warminster, England. (Photo by Matt Cardy/Getty Images)

Clearing skies await a tripod-toting photographer looking for a spot to capture the early-morning light at Portland Head Light, Thursday, January 17, 2013, in Cape Elizabeth, Maine. (Photo by Robert F. Bukaty/AP Photo)