Couples take part in the “Love and Challenge Marathon” in Hanoi, Vietnam, 16 August 2015. Fifty couples, who are going to get married, participated in the event which is held the fifth time. This year, the winners of the marathon received a honeymoon trip to Malaysia. (Photo by Luong Thai Linh/EPA)

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)

Two hippopotamus are fed with pumpkins at the Hanoi Zoo, in Hanoi, Vietnam, 25 October 2018. The zoo has been the home for more than 800 animals of over 90 different species, including three hippopotamus, since it was built in 1976. (Photo by Luong Thai Linh/EPA/EFE)

A Vietnamese cosplayer poses as police officer character from the game during the League of Legends (LOL) Mid-Season Invitational 2019 play-in group stage, in GG Stadium, Ho Chi Minh, Vietnam May 5, 2019. (Photo by Reuters/Kham)

Republic of Korea Air Force's (ROKAF) aerobatic unit “Black Eagles” maneuver their T-50B aircraft as they perform an air show at Clark Air Base on March 03, 2024 in Pampanga, Philippines. The Republic of Korea Air Force's (ROKAF) aerobatic unit “Black Eagles” is in the Philippines to conduct a series of air shows to mark the 75th anniversary of diplomatic relations between the Philippines and South Korea. (Photo by Ezra Acayan/Getty Images)

A hot air balloon depicting a dog that participates in the International Hot Air Balloon Festival, flies over Leon, Guanajuato state, Mexico, on November 14, 2020, amid the COVID-19 coronavirus pandemic. The festival, in which 100 air balloons participate, was held without spectators to avoid crowds and prevent contagion. (Photo by Ulises Ruiz/AFP Photo)

Protesters wear gas masks in the front of the Romanian Environment Ministry in Bucharest March 4, 2019, to demand better air. Dozens of people holding placards reading “Our children don't breath air anymore” gather in the front of the Environment Ministry to ask for better breathable air in Bucharest. (Photo by Daniel Mihailescu/AFP Photo)

A man takes pictures at the finish line during the Colour Run at Centennial Park in Sydney August 25, 2013. According to organizers, 15,000 runners registered to complete the 5km (3 miles) course in Centennial Park on Sunday, being covered in blue, pink, orange and yellow powder on their way to the finish line. (Photo by Daniel Munoz/Reuters)