Costa Rica will celebrate the 11th Festival of the Stone Spheres from Friday to Sunday, the National Museum said Sunday.

The festival, which will take place in the southwestern Osa Peninsula, commemorates the country's more than 300 ancient stone spheres, which in 2014 were added to the list of World Heritage Sites of UNESCO (the United Nations Educational, Scientific and Cultural Organization).

The festival "is a cultural event where the spheres (and) archaeological, historical and sociocultural heritage are valued and commemorated," Carlos Morales, an anthropologist with the National Museum, said in a press release.

The festival will feature a variety of cultural, culinary and sporting events, as well as the exhibition and sale of regional handicrafts, said the museum.

Located at the Palmar Sur archaeological site, the perfectly round stones -- sculpted from a kind of coarse basalt-like rock -- range in size from 10 centimeters in diameter to 2.5 meters, and can weigh as much as 15 tons.

Costa Rica's enigmatic spheres, some of which date from 600 A.D., have puzzled anthropologists since they were first discovered in the 1930s by the United Fruit Company, an American corporation that traded in tropical fruits, when it was clearing jungle for banana plantations.

According to www.world-mysteries.com, the spheres are "still considered a great unsolved archaeological mystery," since their exact purpose has never been unveiled.