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)

An actress performs in a puppet theater show at an UNRWA school in Burj al-Barajneh in Beirut May 14, 2015. The Arab Puppet Theatre Foundation (APTF) is touring the 68 schools of the UN refugee agency's UNRWA and performs for all 39,000 Palestinian students in Lebanon, in a project with UNICEF and UNRWA. (Photo by Mohamed Azakir/Reuters)

Chinese honor guards prepare for the arrival of Palestinian President Mahmoud Abbas and China's President Xi Jinping at the Great Hall of the People in Beijing Wednesday, June 14, 2023. (Photo by Jade Gao/Pool Photo via AP Photo)

A Palestinian woman takes a picture of a member of the Israeli security forces as he takes her picture in a street in Jerusalem on December 16, 2017, as demonstrations continue to flare in the Middle East and elsewhere over the US president' s declaration of Jerusalem as Israel' s capital. (Photo by Ahmad Gharabli/AFP Photo)

Paramedics carry an injured woman out from a subway station after a rush-hour subway train derailment, to be transported by a medical helicopter in Moscow, Russia, on Tuesday, July 15, 2014. A rush-hour subway train derailed in Moscow Tuesday, killing 20 people and injuring at least 150, emergency officials said. Several cars left the track in the tunnel after a power surge triggered an alarm, which caused the train to stop abruptly. (Photo by Ivan Sekretarev/AP Photo)

American artist Robert Wechsler has realized a series of sculptural cubes made from thousands of pennies titled “The Mendicant“. Cubes achieved by notching and joining pennies in perfect orientation to one another. Joined at perpendicular angles, the coins create a lattice structure allowing tunnel like passages of light from certain angles. As one moves around them, the cubes seem to fluctuate from material to ethereal. The number of pennies increases exponentially with the size of the cube. Pictured here are three cubes differentiated with subtitles indicating the exact quantity used.

A competitor reacts ahead of Tough Guy Mudathon event in Perton, Britain, 04 February 2018. The original event which started in 1987 raises money for charity and challenges thousands of international competitors with a cross-country run followed by an assault course consisting of 20 obstacles including water, fire and tunnels. (Photo by Nigel Roddis/EPA/EFE)

A competitor reacts as she takes part in the “Tough Guy” adventure race near Wolverhampton, central England, on January 29, 2017. The Tough Guy event, which is being held for the final time in its 30th year, challenges thousands of competitors to run a gruelling course whilst negotiating over 200 obstacles including: water, fire, and tunnels. (Photo by Oli Scarff/AFP Photo)