At the end of a dark earthen trail in the Peruvian Amazon stands a round structure with a thatched roof that appears to glow from within. In the Temple of the Way of Light, as it is known, indigenous healers called Onanya teach visitors about the therapeutic uses of ayahuasca, a hallucinogenic brew that’s been used by locals for thousands of years. Across the Atlantic, researchers in an ornate blue-tiled hospital in Barcelona, Spain are studying ayahuasca’s