The Basilica houses a special wooden statue of Christ. Here is the story:
One day, shortly after the founding of the city (in a date unknown and unspecified), an Indian woman who had recently been converted to Christianity (who has no recorded name) was washing clothes in the river. Suddenly, she saw a small wooden statue if Christ float by. She grabbed it and went home and planted it in the dirt floor of her room. Upon awakening, she discovered that the Christ statue had grown.
Soon, people were coming to see the Cristo de las Aguas (Christ of the Waters), as it became called. People began worshipping it and adoring it, kissing it, touching it, etc.
Soon, the archbishop of Popayán heard of the statue and became angry. He ordered that it be burned. The story goes that in 1665, the statue was thrown into a fire at the order of the bishop, however, the statue did not burn. Instead it sweat water and sulphur and was left blackened by the experience. People then began to worship the statue even more. In 1783, the official history of the statue was recorded and sent to Rome. There Pope Pius (Pío) the VI returned 22 apostolic briefs which state that worshippers can receive "abundant indulgences (meaning release of the penalty due to sin) by being devout pilgrims" to the statue. A copy of this papal document can be found in the Basilica.
Today, if you go to the Basilica, you will see worshippers bringing bags or bottles of water to the Basilica. These are then placed in front of the statue for a few minutes and money deposited in the box. The water is then thought to be pure and blessed.