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 Muslim woman prays at the Al Meroz hotel in Bangkok, Thailand, August 29, 2016. Predominately Buddhist Thailand has opened its first halal hotel as hopes to attract more Muslim visitors and boost one of the few bright spots in its economy. (Photo by Chaiwat Subprasom/Reuters)

Roof-topping enthusiast Daniel Lau takes a selfie with high-rise buildings down below as he stands on the top of a skyscraper in Hong Kong, China on August 15, 2017. A craze that began in Russia has now taken hold in Hong Kong, one of the world's most vertical cities. Mr Lau said he had been inspired by Russian climbers and that he was unafraid of the vertiginous heights he scales. (Photo by ImagineChina/Rex Features/Shutterstock)

Muslim girls are seen after prayers, in Lagos, Nigeria, Friday, July 31, 2020. Small groups of pilgrims performed one of the final rites of the Islamic hajj on Friday as Muslims worldwide marked the start of the Eid al-Adha holiday amid a global pandemic that has impacted nearly every aspect of this year's pilgrimage and celebrations. The last days of hajj coincide with the four-day Eid al-Adha, or “Feast of Sacrifice”, in which Muslims slaughter livestock and distribute the meat to the poor. (Photo by Sunday Alamba/AP Photo)

A man runs to help a woman as they attempt to shelter in a locked convenience store during heavy wind and rain as typhoon Maysak hits the Haeundae Beach area of Busan, South Korea, on September 3, 2020. Flights were grounded in South Korea and storm warnings issued on both sides of the Korean peninsula as a typhoon forecast to be one of the most powerful in years made its approach. (Photo by Ed Jones/AFP Photo)

A protestor is detained following the grand jury verdict on September 23, 2020 in Louisville, Kentucky. Protesters marched in the streets after a Kentucky grand jury indicts one of the three officers involved in the killing of Breonna Taylor, who was fatally shot by Louisville Metro Police officers during a no-knock warrant at her apartment on March 13, 2020 in Louisville, Kentucky. (Photo by Brandon Bell/Getty Images)

Alejandro Ccasa prays after waiting three days next to an empty oxygen tank for his uncle who has COVID-19 outside a refill shop where he is the first in line before it opens in Callao, Peru, early Tuesday, February 2, 2021. Ccasa said his family has one large tank and it gives about four hours of oxygen therapy. (Photo by Martin Mejia/AP Photo)