Teeming with images of spectacular underwater scenes from around the world, Call of the Blue is the culmination of a five-year project by the photographer and ocean conservationist Philip Hamilton. This groundbreaking book includes contributions from acclaimed scientists and ocean “guardians”, who reveal what drove them to answer the call of the blue. (Photo by Philip Hamilton/The Guardian)

A newlywed couple dangling from a cliff face poses for wedding photos at the Chaya Mountain scenic spot on November 11, 2017 in Zhumadian, Henan Province of China. Chaya Mountain scenic spot was the shooting place for TV series “Journey to the West” and working staff dressed as main characters in this TV series to send the blessing to the newly-weds. (Photo by Sipa Asia/Rex Features/Shutterstock)

A Kurdish female fighter from the People's Protection Units (YPG) gestures as she carries her weapon near al-Hawl area where fighting between Islamic State fighters and fighters from Democratic Forces of Syria are taking place in south-eastern city of Hasaka, Syria November 10, 2015. (Photo by Rodi Said/Reuters)

The Mexico – United States barrier – also known in the United States as the border fence, rotted fence or border wall – is actually several separation barriers designed to prevent illegal movement across the Mexico – United States border.

A general view of the residential area is pictured during dusk at Jodhpur in Rajasthan, April 5, 2015. Jodhpur, also known as the blue city in the desert Indian state of Rajasthan, which residents say originally, was used to show where the highest caste of priestly Hindus live, who wanted to set them apart from the rest of the population. Later the rest of the population followed suit. Another reason for the city to be blue is to keep the buildings cool during the summers, local residents said. (Photo by Adnan Abidi/Reuters)

Chefchaouen or Chaouen is a city in northwest Morocco. It is the chief town of the province of the same name, and is noted for its buildings in shades of blue.