text: Concealed and protected against atmospheric changes for 17,000 years , these awe-inspiring frescoes and engravings of bulls , horses , ibex , bison , and deer were discovered by four teenagers chasing a dog in 1940 .
  
  ###
  
  While four teenagers were chasing a dog in 1940 , they stumbled upon ancient frescoes and engravings that have been concealed for the last 17,000 years .