The pugs dressed in Parka jackets in Sonoma County, California. (Photo by Phillip Lauer/Barcroft Media)

The “Strandbeest” sculpture created by Dutch artist Theo Jansen walks at Federation Square on February 1, 2012 in Melbourne, Australia. The 12 metre long, 4 metre high and 2 metre wide structure built of plastic tubes and bottles designed to walk using wind energy will be on display at Federation Square until February 26. (Photo by Scott Barbour/Getty Images)

The original costumes for Star Wars character Darth Vader stand on display at “Star Wars: The Exhibition” at County hall on May 04, 2007 in London, England. (Photo by MJ Kim/Getty Images)

“Winter shapes, Moscow river”. Moscow river at this part is never covered by ice. When the temperature is very low it's possible to see a strong fog. Morning light and pipes of the oli factory creates a fantastic landscape. Photo location: Moscow, Russia. (Photo and caption by Sergey Rumyantsev/National Geographic Photo Contest)

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)