Huge Granite Spheres

Where do they come from?

In Costa Rica, especially in the southern regions, you can find some carefully worked huge granite spheres. Some are up to 2 meters big. Nobody knows what they mean, there are many speculations, even aliens play a role. For example, in  Sierpe, where you get into the boat to Drake Bay and Corcovado National Park, you can find many of those balls.