It is already one of the world’s most iconic cities, but this incredible collection shows how much Paris has changed over the course of the past century. The collection, by French photographer Julien Knez, shows Paris in the 1940s against a backdrop of how the same places look today. Knez says he put the striking collection together to celebrate the 71st anniversary of the city’s liberation from Nazi control in August 1944. Here: Soldiers outside the Hotel De Ville in the 1940s. (Photo by Julien Knez/Caters News)

Beltane Fire Society performers celebrate the coming of summer by participating in the Beltane Fire Festival on Calton Hill April 30, 2019 in Edinburgh, Scotland. The event celebrates the ending of winter and is a revival of the ancient Celtic and Pagan festival of Beltane, the Gaelic name for the month of May. This years festival was highlighting climate change, with the central character The May Queen being seen to express her rage at the damage done to Earth. (Photo by Jeff J. Mitchell/Getty Images)

Somali women sing as they celebrate the election of President Mohamed Abdullahi Mohamed in the streets of Somalia's capital Mogadishu, February 9, 2017. This election is important because it may establish a pattern of peaceful change of government as well as continue to grow Somalia’s institutions especially for a country that has not heard a stable government for more than two decades. (Photo by Feisal Omar/Reuters)

Kalei Ferrin,3, holds a sign up in support of gay rights during the San Diego gay pride parade July 16, 2011 in San Diego, California. About 200 active-duty troops and veterans from every branch of the military participated for the first time in the march as the ban on the government policy on homosexuals serving in armed forces, or “Don't ask Don't Tell”, remains in flux in the justice system. (Photo by Sandy Huffaker/Getty Images)

Luis Hernan was always curious about how wireless technologies like radio are transmitted through the air. So after finishing up his studies in architecture, computer science, and design, Hernan decided to research these invisible signals through a PhD at Newcastle University. Hernan set up a system that turned the wireless signals around him into colourful, ghostlike images using long-exposure photography, allowing people to see the strength of the signals around them. (Photo by Luis Hernan)

The Y-40 Deep Joy is the worlds deepest pool. Y-40 is projected by Architect Emanuele Boaretto and supported by the “Boaretto Group Hotel and Resort”. The name Y-40 is inspired by mathematical symbols. “Y” is the ordinate axis of the Cartesian system and “–40” means the world's record depth or our pool- that is 40 meters underground. (Photo by Courtesy Y40 Deep Joy)