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)

A group of youngsters dressed as ghouls and zombies for Halloween parade in downtown Lisbon, Portugal, Friday, October 31, 2014. (Photo by Francisco Seco/AP Photo)

Participants prepare backstage before the 5th “Strongo Cup” open amateur bodybuilding tournament at the State Opera and Ballet Theatre in Russia's Siberian city of Krasnoyarsk, November 1, 2014. Participants from all over Russia took part in the tournament competing in bodybuilding, body fitness and bikini fitness disciplines. (Photo by Ilya Naymushin/Reuters)

Model Yasmine Petty arrives on the Life Ball plane on May 15, 2015 in Vienna, Austria. The Life Ball, an annual charity ball raising funds for HIV & AIDS projects, will take place on May 16, 2015 at the city hall in Vienna. (Photo by Monika Fellner/Getty Images)

“A girl arrives at the parking lot wearing tiny leather shorts and sits on the back of a bike with a horse power of more than 1,000 CC. Next to her a man gets ready to ride, wearing a skeleton mask. It’s more than a fashion show, it’s an extravaganza on two wheels along Chinese roads”. – Carlos Barria. Photo: A couple rides their motorcycle at the Qian Dao Lake rally, on May 11, 2013. (Photo by Carlos Barria/Reuters)

Actress Bella Thorne attends the Teen Choice Awards 2015 at the USC Galen Center on August 16, 2015 in Los Angeles, California. (Photo by Steve Granitz/WireImage)

Emma Watson poses at the winners boards at the Sony Ericsson Empire Film Awards at the Grosvenor House Hotel on March 9, 2008 in London England. (Photo by Dan Kitwood/Getty Images)

A man performs a split as he practices Kung Fu at Beihai Park in Beijing, China August 20, 2017. (Photo by Reuters/China Stringer Network)