A visitor walks inside the initiation well at Quinta da Regaleira in Sintra October 6, 2014. Sintra became the first centre of European Romantic architecture in the 19th century, which influenced the development of landscape architecture throughout Europe. It was classified as a World Heritage Site by UNESCO in 1995. Its monuments are visited by more than 1.5 million of tourists every year, according to local media. (Photo by Rafael Marchante/Reuters)

A Hindu holy man on his way to the annual holy dip at Gangasagar, gestures towards a visitor as he rests at a transit camp in Kolkata, India, Wednesday, January 6, 2016. Thousands of Hindu pilgrims are expected to take the annual holy dip at Gangasagar, where the Ganges River reaches the Bay of Bengal, on the auspicious Makar Sankranti festival day that falls on Jan.14. (Photo by Bikas Das/AP Photo)

Elena from Dresden has her hair ruffled by the wind as she stands on a visitors' platform on the Maintower in Frankfurt am Main, western Germany, during stormy weather on February 22, 2017. (Photo by Arne Dedert/AFP Photo/DPA)

In this photo taken on February 21, 2017, shooting instructor Kim Su- Ryon poses for a portrait at the Meari Shooting Range in Pyongyang Kim is holding a “Paektusan” target pistol, gifted by late North Korean leader Kim Il- Sung. Visitors to the range can pay 10 USD to shoot ten rounds. (Photo by Ed Jones/AFP Photo)

A visitor tries the Segway “S-Pod” motorized chair on the manufacturer's booth during the 2020 International Consumer Electronics Show (CES) at the Las Vegas Convention Center in Las Vegas, Nevada, USA, 08 January 2020. (Photo by Etienne Laurent/EPA/EFE)

Visitors browse in the starry Art Museum. Shanghai, China, May 13, 2020. The exhibition hall uses a large number of mirror devices, combined with the layout of acousto-optic, to create a visual scene and spatial effect. (Photo by Costfoto/Barcroft Media via Getty Images)

Souvenirs seller smiles during the street market of the “2021 Agrorus” international agricultural fair at the Expoforum exhibition centre in St. Petersburg, Russia, 02 September 2021. The Exhibition opens for visitors until 05 September 2021. (Photo by Anatoly Maltsev/EPA/EFE)

Performers entertain passengers at London Heathrow Airport's T3 on Monday, November 8, 2021, as the US reopens its borders to UK visitors in a significant boost to the travel sector. Thousands of travellers are jetting off on transatlantic flights for long-awaited reunions with family and friends. (Photo by Steve Parsons/PA Images via Getty Images)