Huge Granite Spheres

Where do they come from?

In Costa Rica, especially in the southern regions, you can find some carefuly worked huge granite spheres. There are some up to 2 meters . Nobody knows what they mean, there are many speculations, even the 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.