Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the city of Bihać, Bosnia, was the largest underground airport and military air base in the former Yugoslavia, and one of the largest in Europe. (Photo by Thomas Windisch/Exclusivepix Media)

A view of a large poster depicting Russian opposition leader Alexei Navalny behind bars with a dove freeing him from detention, by an unidentified street artist known as Harry Greb, in downtown Rome, Italy, 25 January 2021. Navalny was detained after his arrival to Moscow from Germany on 17 January 2021. A Moscow judge on 18 January ruled that he will remain in custody for 30 days following his airport arrest. Navalny urged Russians to take to the streets to protest against President Putin's rule. (Photo by Fabio Frustaci/EPA/EFE)

Australian professional boxer Ebanie Bridges after her fight against Shannon Courtenay during the WBA World Bantamweight Title match at Copperbox Arena in London, Britain on April 10, 2021. (Photo by Andrew Couldridge/Action Images via Reuters)

A man walks into the The Life Tabernacle megachurch as local residents attend Sunday service challenging state orders against assembling in large groups to prevent the spread of coronavirus disease (COVID-19) in Baton Rouge, Louisiana U.S., April 5, 2020. (Photo by Carlos Barria/Reuters)

7th August 1941: A Soviet sniper targets the enemy with the telescopic sight on his rifle.

Medical staff react outside Queen Elizabeth Hospital during the Clap for our Carers campaign in support of the NHS, as the spread of the coronavirus disease (COVID-19) continues, in Birmingham, Britain, April 23, 2020. (Photo by Carl Recine/Reuters)

Jeffrey Shiau, 35, a volunteer from the crowd, spits water into the mouth of Sam Kaufman, 27, a performer from the Human Fountains, during a reopening party held as coronavirus disease (COVID-19) restrictions are gradually lifted in Los Angeles, California, U.S. June 15, 2021. (Photo by Cheney Orr/Reuters)

Clouds cover the sky over the Ernst-Taehlmann-Park housing estate after a thunderstorm in Berlin, Germany, Thursday, March 11, 2021. (Photo by Markus Schreiber/AP Photo)