David Pattyn / Landscape of Hills at the Melnik earth pyramids at sunrise, Foothills of Pirin Mountains, South West Bulgaria, April

David Pattyn / The Melnik Earth Pyramids, rock formations, known as hoodoos, situated at the foothills of the Pirin mountain range in south-western Bulgaria, Bulgaria, April

Olga Kamenskaya / Pyramidal ice fragment reflected on the surface of Lake Baikal. Ice fragment acting as a prism refracting light into rainbow. Siberia, Russia, March.

Gerry Ellis / The pyramids of Giza in evening light, Giza, Egypt

Staffan Widstrand / Camel's head with Pyramids of Giza in background. Cairo, Egypt.

Ingo Arndt / Earth pyramids, Renon Plateau, Ritten, South Tyrol, Italy. 2017.

Guy Edwardes / Sand Pyramids in winter, Rozhen, Melnik, Bulgaria, January 2016.

Guy Edwardes / Sunrise at Sand Pyramids, Bulgaria. February 2014

Guy Edwardes / Sand Pyramids, Rozhen, Bulgaria. November 2014

Guy Edwardes / Sand Pyramids, Rozhen, Melnik, Bulgaria. October 2017

Juan Manuel Borrero / Structure II (Great Pyramid), one of the largest Mayan structures. This temple pyramid is built over a smaller pyramid which dates back to 400 BC-250 AD with later extensions added on to the building,...

Juan Manuel Borrero / Structure II (Great Pyramid), one of the largest Mayan structures. This temple pyramid is built over a smaller pyramid which dates back to 400 BC-250 AD with later extensions added on to the building,...

Juan Manuel Borrero / Structure II (Great Pyramid), one of the largest Mayan structures. This temple pyramid is built over a smaller pyramid which dates back to 400 BC-250 AD with later extensions added on to the building,...

Juan Manuel Borrero / Cuauhcalli or House of Eagles, building carved into side of a mountain, from 1501, Malinalco, Mexico, March 2017.

Nick Upton / Sand pyramids and cliff face of heavily eroded, weathered soft sandstone / conglomerate, Miljevina, near Foca, Bosnia and Herzegovina, July 2014.

Aflo / Men riding camels in front of the Pyramids of Giza, UNESCO World Heritage Site, Egypt, October 2010.

Philippe Clement / The earth pyramids of Longomoso / Lengmoos / Monti di Mezzo on the Renon plateau, Dolomites, Italy. July 2010.

Philippe Clement / The earth pyramids of Longomoso / Lengmoos / Monti di Mezzo on the Renon plateau, Dolomites, Italy. July 2010.

John Waters / View of the Pyramid Complex, Meroe, north Sudan

Philippe Clement / Pyramids of Euseigne, formed by erosion of soft rock below hard rock, Valais, Switzerland, July 2009

Philippe Clement / Pyramids of Euseigne, formed by erosion of soft rock below hard rock, Valais, Switzerland, July 2009

Philippe Clement / Pyramids of Euseigne, formed by erosion of soft rock below hard rock, Valais, Switzerland, July 2009

Shattil & Rozinski / Pyramids, Giza, Egypt, 1995

Shattil & Rozinski / Pyramids at sunrise, Giza, Egypt, 1995

Shattil & Rozinski / Pyramids, Giza, Egypt, 1988

Shattil & Rozinski / The Sphinx with Khafre pyramid in the background, Giza, Egypt, 2007

Shattil & Rozinski / The Sphinx with Khafre pyramid in the background, Giza, Egypt, 2007

Shattil & Rozinski / Pyramids at sunrise, Giza, Egypt, 1989

Shattil & Rozinski / Pyramids at sunrise, Giza, Egypt, 1992

Shattil & Rozinski / Pyramids at sunrise, Giza, Egypt, 1995

Juergen Freund / Pyramids of salt at the Leslie Salt Company's operations. Over 2 million tonnes of solar produced salt are exported out of the area each year. Port Hedland, West Australia

John Downer / Domestic donkey {Equus asinus} with ancient pyramids of Giza in background, Egypt

John Downer / Domestic donkey in front of the famous Pyramids of Giza, Egypt

Staffan Widstrand / Looking across to Pyramids of Giza, ancient wonder of the world, with Cairo in background, Egypt, North Africa

Martin Gabriel / Soil pyramids (pinnacles) caused by erosion Lombardia, Ritten, nearr Bolzano, Italy

Kim Taylor / The Great Pyramids of Giza

Daniel Gomez / Pyramid of the Sun, Teotihuacan Aztec archaeological site, Mexico.

Daniel Gomez / Pyramid of the Sun, Teotihuacan - Aztec archaeological site. Mexico.

Kim Taylor / The Pyramids of Giza, Eygpt.

Gerry Ellis / Modern Egyptians riding domesticated camels across desert near the pyramids of Giza at sunset, Cairo, Egypt

Norbert Wu / Camel and rider in front of the Pyramids at Giza, Cairo, Egypt

Mitsuaki Iwago / Domestic Cat (Felis catus) statues lined up in the desert with Egyptian pyramids in the background, Egypt

Dan Rees / The Sphinx, Cairo, Egypt with BBC NHU film unit

Dan Rees / Cairo and the Pyramids, Egypt

Staffan Widstrand / The pyramids of Giza, near Cairo, Egypt.

Christian Ziegler / Small leaf particles protect the soil under them from erosion, creating tiny pyramids of protected soil, Barro Colorado Island, Panama

Norbert Wu / The Sphinx and Great Pyramids, Giza, Cairo, Egypt

John Downer / Dromedary camel near The Pyramids (Camelus dromedarius) Egypt

Guy Edwardes / Sun rising behind Sand Pyramids at dawn, Melnik, Bulgaria, October 2017.

Milan Radisics / Aerial view of solar panels on top of a coal ash pyramid in East-Central Europe. After coal is burned in power plants, the waste ash is stacked and compacted into large pyramids, which may eventually...

Milan Radisics / Aerial view of coal ash pyramid in East-Central Europe. After coal is burned in power plants, the waste ash is stacked layer-by-layer and compacted into large pyramids, which may eventually be covered...

Milan Radisics / Aerial view of coal ash pyramid in East-Central Europe. After coal is burned in power plants, the waste ash is stacked layer-by-layer and compacted into large pyramids, which may eventually be covered...