Hundreds of near-perfect stone spheres scattered through the lowland forest and banana fields of the Diquís Delta. They are gabbro and granodiorite, carved by the Chibchan-speaking people who lived along the Térraba river between roughly 600 and 1500 CE. The largest is more than two metres across. Nobody is sure what they were for. They sit, very quietly, and ask the question for you.