ALTAMIRA, SPAIN—The cave at Altamira, where bison and horses were painted and carved into the limestone some 22,000 years ago, was closed to visitors in 2002 due to the grown of algae-like mold on the cave walls. But as part of a new study, five randomly chosen visitors a week have been allowed to enter the cave wearing special protective suits since late last February. The goal of the study is to determine “if there is a form of public visiting that is compatible with the adequate conservation of Altamira,” José Antonio Lasheras, director of the Altamira museum, told The New York Times. The results of the investigation are due in September. Some scientists are concerned that the experiment will endanger the rock art in order to promote tourism. “All the data indicate the fragility of the cave and its propensity to suffer a fungal infection if it is opened to visits,” said Cesáreo Sáiz Jiménez, a research professor at the Spanish National Research Council.