Fountain of youth

The fountain of youth is a mythical water source said to revert the effects of time on a person's body. Its location was a mystery through history, being a focus of philosophy and exploration for centuries. The place's description would change through time, at some points becoming an object instead of a location. It's location, however, was never found.
Many claim the appearance of the myth to have happened in ancient Greece, before the Macedonian era. Many classical phylosophers like Plato or Aristotle mention the place as a glorious, holy, almost divine place, where the flowing water could cure extreme terminal ilnesses and revitalize the human body.

Age of Discovery

Upon arrival in the new world, many explorers repeatedly asked natives and investigated tirelessly the American continent in search of the fountain, being sometimes mentioned as a reason why the Colombian interior and the deepnesses of the Amazonian rainforest were explored to intensively.
Two places have been known to have been mentioned by explorers as the locaiton of the fountain of youth:

Florida

The floridan peninsula was mentioned as the possible location by spanish explorer Ponce de León, near the end of the 16th century, even writting an official document to the king of Iberia inviting him to visit the place.
In 1893, a small touristic attraction opened near Miami, where it was claimed that the original fountain had been found, being marked by a big X in the ground, supposedly made by Ponce de león himself. History records indicate that there is some plausibility to this story, however, the water had no curative effects.

El Dorado

After the leyend of El Dorado was made popular in Europe, it was also thought the possibility about the Fountain of Youth being located in the city, reason why regions like Guayana were explored time and time again, without sucess.

The Ruby Cup

During the Age of Pirates the myth became extremely popular, not as a location, but as a golden cup with a big red duby on the front, known as the Ruby Cup. It quickly spread to Europe and the new world, sometimes being called the "Red Cup" or the "Blood Cup". Some versions of the story depicted a cup that turned water into revitalizing blood, while others claimed it to transform water into rum or other alcoholic beverages.
Many movies have depicted multiple versions of the Ruby Cup, The Bucaneers' (1988 movie) version being the most accurate to history, mentioning the myth of a Red Golden Cup that turned water into revitalizing rum. In this version it is said that the cup's location would be found the day someone came across the smell of rum on a beach there there was no clear source of it, being the buried cup the creator of the rum and turning the beach's water around it into rum too.

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Credits: Top image: Colombian flag - thevaccinereaction.org, modified by Colombus