Bonbibi, Treehouse Point, Fall City, WA. The Bonbibi is balanced on two steel yokes. The yokes spread out the load and allow for tree growth and movement in the wind. A small deck hangs from the beams below and uses the treehouse itself to shelter guests. (Photo by Pete Nelson)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)

Yenny Mamani "Marta la Altena", top, grabs Leonor Cordova "Angela la Simpatica" in a hold during a Bolivian wrestling Cholitas fight in Madrid, Spain, Thursday October 8, 2015. (Photo by Paul White/AP Photo)

An aerial view shows the 11/19 pit and twin slag heaps at the former coal mine site in Loos-en-Gohelle, northern France, November 1, 2015. Loos-en-Gohelle, a town of 7000 inhabitants in the North of France, marked by the closure of coal mines in 1970, has demonstrated a successful transition from coal to a green economy. (Photo by Pascal Rossignol/Reuters)

These stunning photographs show the changing face of a majestic centuries old Kazakh pastime tradition that still lives in the lands of mongolia – eagle hunters. Photo: 13 year old Irka Bolen with his eagle. Tradition wise, when a boy turns 13, then are strong enough to hold the weight of a fully grown eagle. (Photo by Asher Svidensky/Caters News)

(L-R) Edmea Pereira, 69, Elsa Rodrigues, 61, and Osmidio Conde, 71, take part in their surf class in Santos, Sao Paulo state, Brazil, March 16, 2016. When work is up, surf is up in Brazil, as a group of retired citizens take to the waves in keep-fit, keep-young sessions at a surf school in the city of Santos. The classes are run for free, three times a week at the Cisco Arana school, which aims to prove that age is just a number. (Photo by Nacho Doce/Reuters)

An injured person is seen after an earthquake hit Port-au-Prince, Haiti, Tuesday, January 12, 2010. A 7.0-magnitude earthquake, the largest ever recorded in the area, rocked Haiti on Tuesday. (Photo by Jorge Cruz/AP Photo)

The buildings of the banking district are seen through thousands of rain drops on a glass railing in central Frankfurt, Germany, Wednesday, January 11, 2017. (Photo by Michael Probst/AP Photo)