Although this is a bit out of my area of expertise, I highly recommend that you check out Carmen Drahl's article on the re-opening of Spain's Altamira Cave, known for its prehistoric wall paintings, after being closed in 2002 because visitors were introducing bacteria to the cave walls that damaged the paintings. Be sure to check out the infographic at the end of the article, too.
The cavern that houses Spain’s most celebrated prehistoric art is on the mend from a microbial infestation that closed it to the public. A push from regional government officials to reopen Altamira Cave to visitors has researchers who worked to improve its condition worried that their efforts will be undone (Science, DOI: 10.1126/science.1206788). But like the bacterial colonies dotting the storied cave’s walls, the scientific and ethical issues that will determine its fate are colored in shades of gray.
Nestled underground near a village in northern Spain, Altamira Cave contains astonishingly lifelike renderings of fawns, horses, and bison painted on its ceilings. The multicolored likenesses, more than 14,000 years old, are recognized as a pinnacle of Paleolithic rock art. The United Nations Educational, Scientific & Cultural Organization (UNESCO) declared Altamira Cave a World Heritage Site in 1985.