The Museo de Altamira, which manages the Altamira Caves in northern Spain—known for their Paleolithic art estimated to be more than 18,000 years old—has determined that allowing a limited number of tourists to visit the site will not damage the fragile paintings. As reported by the Art Newspaper, the caves, which recently began welcoming the public on an experimental basis for the first time since 2002, will continue the practice through at least February of next year.

The caves were closed when mold began growing on the paintings inside the caves, which were designated a UNESCO World Heritage Site in 1985 and have been dubbed the “Sistine Chapel of Palaeolithic Art.” Conservators were concerned that body heat and moisture from tourists was accelerating the mold’s growth and the deterioration of the painting.

“The people who go in the cave have the bad habit of moving, breathing, and perspiring,” concluded a 2010 report that advised against reopening the caves. The site formerly hosted as many as 3,000 people per day. Nevertheless, shutting down such a major attraction (although there is a carefully constructed replica nearby) is undoubtedly bad for Spanish tourism, so they are trying again.

Since the caves reopened in late February of this year, five lottery winners have been admitted for less than an hour each week, giving a conservation team the chance to assess their impact on the paintings. To date, their findings have been positive. Gaël de Guichen, the head of the research team, described the effect of the small groups as “virtually imperceptible,” telling El Pais that “the main danger for the paintings comes from nature and that will continue. There is very little we can do.”

The study will continue for another six months, at which time a long-term decision will presumably be made. If De Guichen has his way, however, it seems safe to say that tourists will have the chance to view the prehistoric art at Altamira for years to come. As he told El Pais, “a work of art is not to be kept away in a safe.”