In this photo taken Tuesday, October 14, 2014, skulls and bones are stacked at the Catacombs in Paris, France. The subterranean tunnels, stretching 2 kilometers (1.24 miles), cradle the bones of some 6 million Parisians from centuries past and once gave refuge to smugglers. The site used to close at 5 p.m., but is now staying open until 8 p.m. The change is mainly aimed at allowing more people to visit and reducing long lines, since it can only hold a limited number of people at a time and visits can't be reserved in advance. (Photo by Francois Mori/AP Photo)

Pottery heads by artist Johan Thunell are displayed at The Affordable Art Fair on March 15, 2012 in London, England. 120 galleries are displaying works costing from £40 – £4000. Photography, paintings, prints and sculptures are on sale from 15–18th March 2012. (Photo by Peter Macdiarmid/Getty Images)

A racegoer enjoy the atmosphere following 2016 Derby Day at Flemington Racecourse on October 29, 2016 in Melbourne, Australia. Women attendees weren’t afraid to show off some skin as the warm summer weather arrived in Australia. (Photo by Splash News and Pictures)

Animal rights activists covered with fake blood sit on the floor during a protest against the use of animals in research to mark World Day for Animals in Laboratories in central Madrid April 24, 2014. The sign reads, “How many rabbits do your shampoo kill?”. (Photo by Andrea Comas/Reuters)

An infrared portrait from NASA's Spitzer Space Telescope which shows generations of stars is seen in this undated NASA handout image released February 14, 2013. In this wispy star-forming region, called W5, the oldest stars can be seen as blue dots in the centers of the two hollow cavities (other blue dots are background and foreground stars not associated with the region). Red shows heated dust that pervades the region's cavities, while green highlights dense clouds. (Photo by NASA/Reuters/JPL-Caltech/Harvard-Smithsonian/Handout)

A picture shows the full moon during a “blood moon” eclipse over the temple of Apollo in Corinth on July 27, 2018. The longest “blood moon” eclipse this century began on July 27, coinciding with Mars' closest approach in 15 years to treat skygazers across the globe to a thrilling celestial spectacle. (Photo by Valerie Gache/AFP Photo)

The reflection of a man dressed as Hindu deity of death Yamaraj (R) to raise awareness about the coronavirus is seen on the wing mirror of a vintage car during a government-imposed nationwide lockdown as a preventive measure against the COVID-19 coronavirus, in Kolkata on April 24, 2020. (Photo by Dibyangshu Sarkar/AFP Photo)

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)