National Geographic has created “Air, Land & Sea: the 50 greatest wildlife photographs” exhibition. Here: CT4 Crocodile cave on the Salamat river. Set up with Nathan Williamson last chip rain came while we were with the nomads. (Photo by Michael Nichols/National Geographic)

Members of the Palestinian Hamas security forces show their skills as they take part in a graduation ceremony in Gaza City on January 22, 2017. (Photo by Mahmud Hams/AFP Photo)

Russian honour guards wearing protective masks attend the opening ceremony of the 6th International Military Technical Forum “Army 2020” and Army Games in the military Patriot Park outside Moscow on August 23, 2020. (Photo by Kirill Kudryavtsev/AFP Photo)

People dressed in the historic uniforms of the Imperial Russian army take part in a re-enactment of the 1812 Battle of Berezina, to mark the 204th anniversary of the battle, near the village of Bryli, Belarus, November 27, 2016. (Photo by Vasily Fedosenko/Reuters)

Afghanistan's interior ministry special forces demonstrate their skills during a military exercise in Kabul, Afghanistan, Thursday, April 2, 2015. Afghanistan's security forces took over full responsibility for the country's security on January 1, 2015. (Photo by Massoud Hossaini/AP Photo)

A two-horse team street cleaner, with sprayer, squeegee, and roller at rear. New York, between ca. 1910 and ca. 1915. (Photo by NYC Municipal Archives)

Ultra Orthodox Jewish men watch a bonfire during the Jewish holiday of Lag Ba-Omer in Jerusalem's Mea Shearim neighbourhood April 27, 2013. Israelis celebrate the Jewish holiday of Lag Ba-Omer, which marks the end of a plague in the Middle Ages that killed thousands of disciples of a revered rabbi in the holy land, by lighting bonfires across the country. (Photo by Ronen Zvulun/Reuters)

Bill Moreau watches as the Black Forest fire burns near his house near Black Forest Road Tuesday afternoon, June 11, 2013, near Colorado Springs, Colo. The Black Forest Fire was one of at least three significant wildfires burning in Colorado amid gusty winds and record-breaking hot, dry weather. (Photo by Christian Murdock/AP Photo/The Colorado Springs Gazette)