( CNN ) -- It 's been called the `` Sistine Chapel of paleolithic art , '' and it 's been closed to the public for more than a decade -- until now . Yesterday , five members of the public who entered a draw were given a guided tour of the extraordinary prehistoric paintings within the Altamira cave in northern Spain . The vivid images , up to 20,000 years old , depict an extinct species of bison , wild boar and other animals , along with sprayed hand prints and engravings . The visit of a lucky few to the twisting , 300-meter-long cave -- sealed in pristine condition by a rockfall for 13,000 years before its discovery in 1879 -- serves a wider purpose beyond their own amazement , however . Small groups drawn from visitors to the nearby museum on one randomly selected day each week until August will be used to test any destructive impact a human presence might have on the ancient paintings through changes in humidity , temperature , CO2 levels and microbiological contamination , the Guardian reports . Wearing protective clothing , masks and shoes , the visitors get a tour of the cave lasting just over half an hour , only a portion of which is to be spent gazing at the rock art . The results will help to determine whether the cave , in the Cantabria region , should be reopened to the public permanently -- a boon to the local economy but an outcome opposed by some scientists . Dismissed as forgeries . Revealed in the late 19th century by an amateur archaeologist led to the site by his eight-year-old daughter , the charcoal and ochre animal studies and other figures at Altamira were at first dismissed as forgeries . The images , in some cases exploiting the cave 's natural contours to create an even more lifelike effect , were deemed too sophisticated to have been produced by ancient humans . It was only 20 years later , when the Altamira paintings could be compared with other recent prehistoric finds , that their extreme antiquity was accepted -- and the understanding of early humans transformed . The Altamira cave was first closed to the public in 1977 , when the body heat and CO2 from 3,000 daily visitors were found to be damaging the paintings . The site was subsequently reopened to restricted numbers , creating a waiting list of up to three years . In 2002 , Altamira -- a Unesco World Heritage Site since 1985 -- was closed a second time when body heat , light and moisture were found to be causing a green mold to grow on the ancient works . Campaign to reopen cave . Since then the Cantabrian regional administration has pushed for Altamira to be opened to the public once more . The goal was to achieve a `` balance '' between preserving the rock art and making a vital part of Spain 's heritage accessible , the director of the Altamira Museum , JosÃ© Antonio Lasheras , told CNN . However , the Spanish government 's main research body opposes the reopening of the cave . `` The consequences of doing so are incalculable , '' Sergio SÃ¡nchez Moral , lead researcher at the Spanish National Research Council , told Publico.es . For the past decade , visitors to Altamira have had to be content with replicas of the paintings -- mainly those in the cave 's main chamber -- located a short walk away in in the museum . `` The original [ paintings ] can be thrilling because the feeling of entering the cave is difficult to reproduce , '' Lasheras said . `` But people have also felt excited going through the replica . '' The museum also has a permanent exhibition called `` The Times of Altamira , '' including furniture made of animal bone and antler , depicting life during the paleolithic era . Museo de Altamira , Avda . Marcelino Sanz de Sautuola , 39330 Santillana del Mar , Cantabria , Spain ; +34 942 818 005/815 .
` ` Sistine Chapel of paleolithic art '' reopens to small visitors . Effect of sunlight on city 's humidity , yet to be measured . Site discovered by amateur archaeologist and his daughter in 1879 .