Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

“Are you here for the Winery Tour?” This is a Western Grey Kangaroo caught lounging in the wineries of the Adelaide Hills in South Australia. This past Autumn has been a spectacular time for wildlife viewing and I got lucky to spot this guy while mountain biking in the hills. Such a funny stance it just begs the question... Have you been drinking? ...and or... Are you here for the Winery Tour? Such a spontaneous moment I figured it would be perfect for an entry. I hope you like it! Cheers. Photo location: Adelaide Hills, South Australia, Australia. (Photo and caption by Greg Snell/National Geographic Photo Contest)

Men slide in the mud during the Boryeong Mud Festival at Daecheon Beach in Boryeong, South Korea, Saturday, July 22, 2017. The 20th annual mud festival features mud wrestling and mud sliding. (Photo by Ahn Young-joon/AP Photo)

A person dressed as an astronaut walks past a man stopping traffic on a pedestrian crossing outside the Sydney Exhibition Centre September 13, 2014 where the science-fiction convention called “Oz Comic-Con” is currently being held. The two-day convention showcases “pop culture”, and includes appearances by actors from science-fiction movies and television shows. (Photo by David Gray/Reuters)

A spectator shows off her green, white and gold eyelashes as the annual Saint Patrick's day parade takes place on March 17, 2018 in Dublin, Ireland. Dublin hosts the largest Saint Patrick's day parade in the world with a route spanning 2.5 km. The Irish annals for the fifth century date Patrick's arrival in Ireland in the year 432 with the patron saint of Ireland's remains believed to be buried at Down Cathedral in County Down. (Photo by Charles McQuillan/Getty Images)

A police cadet casts her vote in the presidential election in Moscow, Russia, Sunday, March 18, 2018. Vladimir Putin headed to an overwhelming win in Russia' s presidential election Sunday, adding six years in the Kremlin for the man who has led the world' s largest country for all of the 21 st century. (Photo by Pavel Golovkin/AP Photo)

A believer dressed as a “diablo” (devil) jumps at the San Blas' (Saint Blaise) procession during the “Endiablada” festival in Almonacid del Marquesado, in central Spain February 3, 2015. In the “Endiablada”, an undated traditional festival in honour of the Candelaria Virgin and San Blas, believers are dressed in colourful costumes, wear a mitre with lead cowbells tied to their waists that ring as they wander around the village and in front of the saints' statues during their processions. (Photo by Susana Vera/Reuters)

In this Thursday, December 1, 2016 photo, Cat Bigney, part of the Oglala Native American tribe, waits on the shore of the Cannonball river for travelers to arrive by canoe at the Oceti Sakowin camp where people have gathered to protest the Dakota Access oil pipeline in Cannon Ball, N.D. So far, those at the camp have shrugged off the heavy snow, icy winds and frigid temperatures. But if they defy next week's government deadline to abandon the camp, demonstrators know the real deep freeze lies ahead. Life-threatening wind chills and towering snow drifts could mean the greatest challenge is simple survival. (Photo by David Goldman/AP Photo)