Vietnam’s Son Doong cave, the largest in the world, could hold a 40-story skyscraper inside. The pristine ecosystem has its own river and jungle. Despite its size, Son Doong wasn’t discovered until 1991. It was lost again for nearly two decades and was fully explored for the first time in 2009. (Photo by Jason Speth/HuffPost)

A view of the start of the 37th Gotland Grand National motocross race in Visby, Sweden on October 24, 2020. (Photo by Soren Andersson/TT News Agency via Reuters)

Revellers celebrate the New Year in Princes Street during Hogmanay street party celebrations in Edinburgh, Scotland January 1, 2015. (Photo by Russell Cheyne/Reuters)

Pope Francis passes past a portrait of himself as he arrives to meet youths in Santo Tomas University in Manila, Philippines, Sunday, January 18, 2015. Francis is in the Philippines on Sunday, the final full day of a weeklong trip that also took him to Sri Lanka. (Photo by Alessandra Tarantino/AP Photo)

A woman wearing a mask to help protect against the spread of coronavirus, tries to communicate with Efe, a cat living in Kugulu public garden, in Ankara, Turkey, Monday, November 30, 2020.Turkey's President Recep Tayyip Erdogan has announced Monday the most widespread lockdown so far amid a surge in COVID-19 infections, extending curfews to weeknights and full lockdowns over weekends. (Photo by Burhan Ozbilici/AP Photo)

People walk in the rainstorm as typhoon Lekima approaches in Shanghai, China on August 10, 2019. The death toll from Typhoon Lekima rose to 49 on August 13 and 21 were still missing after the monster storm wreaked havoc on China's eastern coast, causing huge damage with strong gales and torrential rain. (Photo by Aly Song/Reuters)

Young Lebanese women wearing protective masks and gloves against the coronavirus pandemic, stand on August 5, 2020 amid the rubble in Beirut's Gimmayzeh commercial district which was heavily damaged by the previous day's powerful explosion that tore through Lebanon's capital, resulting from the ignition of a huge depot of ammonium nitrate at the city's main port. Rescuers searched for survivors in Beirut after a cataclysmic explosion at the port sowed devastation across entire neighbourhoods, killing more than 100 people, wounding thousands and plunging Lebanon deeper into crisis. The blast, which appeared to have been caused by a fire igniting 2,750 tonnes of ammonium nitrate left unsecured in a warehouse, was felt as far away as Cyprus, some 150 miles (240 kilometres) to the northwest. (Photo by AFP Photo/Stringer)

A resident looks into a newly-built giant trash can, partially buried underground, next to a street in Taiyuan, Shanxi province November 6, 2014. The trash can, which has a diameter of 1.9 meters and a depth of 2.8 meters, could contain approximately 10 cubic metres of garbage. It was built to replace an open-air garbage dump site, local media reported. (Photo by Reuters/Stringer)