Cratera de Colônia

This guide to Cratera de Colonia in Sao Paulo follows the decades-long puzzle over what carved this three-and-a-half-kilometer ring of high ground south of the city. It opens with the University of Sao Paulo professors who spotted the near-perfect circle in aerial photographs in 1961 and guessed volcano, then follows geologist Victor Velazquez Fernandez back into the swampy basin in 2013 with a microscope and grains of oddly cracked quartz. Stand at the rim and look toward the center the ring surrounds.