Internally displaced Syrian children stand at the entrance of their makeshift shelter that is an underground cave in Om al-Seer, southern Idlib countryside, Syria December 26, 2015. (Photo by Khalil Ashawi/Reuters)

The image of President George Washington is seen on an engraving plate for a one dollar bill at the Bureau of Engraving and Printing in Washington November 14, 2014. (Photo by Gary Cameron/Reuters)

A mother and her daughter paddle during a Stand Up Paddle (SUP) race of the Alpine Lakes Tour, on Europe's biggest underground lake, in St-Leonard, Switzerland, March 10, 2018. SUP is an offshoot of surfing that originated in Hawaii. Unlike traditional surfing where the rider sits until a wave comes, stand up paddle boarders stand on their boards and use a paddle to propel themselves through the water. (Photo by Denis Balibouse/Reuters)

Partially constructed notched burial plots are seen at the construction site of an underground tunnel designated for traditional Jewish burial at the Givat Shaul cemetery, on May 14, 2015, in Jerusalem, Israel. Underground cemetery being built by the Israeli Burial Society in Jerusalem due to a decrease in available land for traditional Jewish burials. (Photo by David Vaaknin/The Washington Post)

A member of staff at Morton & Eden holds an extremely rare early Islamic gold coin on Thursday September 12, 2019, which is expected to fetch £1.4m at auction in London. Measuring a 20mm across, about the size of a modern £1 piece, it is one of the world's rarest and most treasured Islamic gold coins from the first dynasty of Islam, the Umayyad gold dinar dated 105h (723AD). (Photo by Victoria Jones/PA Images via Getty Images)

A woman holds newly designed Indonesia Rupiah banknotes after exchanging her old bills at a Bank Indonesia mobile bank in Jakarta, Indonesia December 19, 2016. (Photo by Fatima El-Kareem/Reuters)