Men slide in the mud during the Boryeong Mud Festival at Daecheon Beach in Boryeong, South Korea, Saturday, July 22, 2017. The 20th annual mud festival features mud wrestling and mud sliding. (Photo by Ahn Young-joon/AP Photo)

Happiness on a Rainy Day by Fardin Oyan, Bangladesh. Winner of the young environmental photographer of the year. Many children in Bangladesh love to bathe and play in the rain. The country, which is flat and occupied by the huge Ganges-Brahmaputra Delta, is exposed to floods, especially during monsoon season. (Photo by Fardin Oyan/2018 Ciwem environmental photographer of the year 2018)

Young Japanese women pose with a green bear costumed person during the 'Earth Parade 2015' in Tokyo, Japan, Saturday, November 28, 2015. Ahead of the U.N. climate change summit in Paris starting this week, about 1,000 citizens and environmental activists took to the streets of Tokyo on Saturday, calling for strong actions to combat global warming. (Photo by Franck Robichon/EPA)

Young women sit at a doorway during the annual San Antonio Abad (Saint Anton Abbott) festival in Trigueros, southwest Spain January 25, 2015. Thousands of people arrived in Trigueros to participate in this annual catching of food and presents, part of a traditional three-day religious festival. (Photo by Marcelo del Pozo/Reuters)

A young Hindu girl sits for a ceremony where she and other girls are worshipped as “Kumari”, or living goddess, during Ram Navami festival, at a temple in Kolkata, India, Saturday, March 28, 2015. Ram Navami marks the birth of Hindu God Rama. (Photo by Bikas Das/AP Photo)

Young people fight for fun with their pillows, during the International Pillow Fight Day at the Place des Grottes, in Geneva, Switzerland, Saturday, April 4, 2015. The annual International Pillow Fight Day takes place in hundreds of cities around the world. (Photo by Salvatore Di Nolfi/AP Photo/Keystone)

A young woman dressed as a zombie takes part in a zombie parade as part of the Brussels International Fantastic Film Festival 2014 in Brussels, Belgium, 12 April 2014. More than a hundred of participants took to the streets of Brussels. (Photo by Ulien Warnand/EPA)

An adult chimp plays with a young chimp at Chimp Haven in Keithville, La., Monday, February 18, 2013. One hundred and eleven chimpanzees will be coming from a south Louisiana laboratory to Chimp Haven, the national sanctuary for chimpanzees retired from federal research. (AP Photo/Gerald Herbert)