A man climbs an artificial wall of ice in the city of Liberec, Czech Republic, February 5, 2019. Every winter since 2013, climbers in the Czech Republic have gathered to tackle the challenge presented by a naturally-forming wall of ice some 20 metres (66 feet) high. REUTERS/David W Cerny

A man climbs an artificial wall of ice in the city of Liberec, Czech Republic, February 5, 2019. Pavel Pfeifer, who organises climbing at the site, said his friends were walking by the cliff and noticed how ice had formed on its surface. REUTERS/David W Cerny

A man climbs an artificial wall of ice in the city of Liberec, Czech Republic, February 5, 2019. They were given permission by authorities in Liberec to manage the site, putting in place safety ropes, renting equipment, and organising climbing courses. REUTERS/David W Cerny

A woman climbs an artificial wall of ice in the city of Liberec, Czech Republic, February 5, 2019. REUTERS/David W Cerny

People climb an artificial wall of ice in the city of Liberec, Czech Republic, February 5, 2019. REUTERS/David W Cerny