A protester holds a poster displaying the message “Get away UK” during an anti-British demonstration in the Iranian capital that resulted in a break in at the British Embassy on November 29, 2011 in Tehran, Iran. (Photo by FarsNews/Getty Images)

Created by Brazilian agency Heads Propaganda, these thought-provoking poster ads draw attention to the fact that many cyclists are knocked down at night due to the lack of respect by the motorists who share their roads.

Shamans perform a ritual of predictions for the upcoming US election with posters of presidential candidates Donald Trump and Hilary Clinton at the Agua Dulce beach in Lima on November 7, 2016. Hillary Clinton and Donald Trump launched into the frenzied final day of their historic fight for the White House Monday, with blow-out rallies in the handful of swing states that will decide who leads the United States. (Photo by Ernesto Benavides/AFP Photo)

A poster of Russian President Vladimir Putin is used as target practice along a trench on the frontline with Russia-backed separatists near Zolote village, in the Lugansk region, on January 21, 2022. Ukraine's Foreign Minister Dmytro Kuleba on January 22, 2022, slammed Germany for its refusal to supply weapons to Kyiv, urging Berlin to stop “undermining unity“ and “encouraging Vladimir Putin” amid fears of a Russian invasion. (Photo by Anatolii Stepanov/AFP Photo)

Alina Serban (L) poses during a photo session for the poster of her show in Bucharest on October 20, 2021. Roma actress and playwright Alina Serban grew up watching TV and going to the theatre without any stories “with or about people like us” – something she set out to change, becoming the first to have her work on the stage of Bucharest's National Theatre. (Photo by Bogdan Dinca/AFP Photo)

A poster advertises the highly anticipated video game, “Call Of Duty: Modern Warfare 3” at a GameStop Corp. store November 6, 2011 in North Las Vegas, Nevada. Video game publisher Activision plans to release the eighth installment in the “Call of Duty” franchise at midnight on November 8. (Photo by Ethan Miller/Getty Images)

People wash in water from a broken water pipeline on the outskirts of Kolkata, India, March 30, 2016. (Photo by Rupak De Chowdhuri/Reuters)

A cenote is a natural phenomenon, a sinkhole in the Earth’s surface. The Yucatan Peninsula in Mexico has an estimated 7,000 cenotes because it is primarily made up of porous limestone. For millions of years, rainfall slowly ate away at the limestone and a huge system of underground caves and caverns was formed. Many filled with water from rain or from the underground water table. When the roof of a water filled cave collapses, a cenote is born. The water found in a cenote may be fresh water, salt water, or both. Structurally it may be completely open, like a lake, almost completely closed with just a small opening at the top, or somewhere in between.