I discovered the portal on an early Sunday walk. Shaded by a copse of trees, the stone triangle steamed in the Derbyshire fog and smelled of ozone. The opening, seven feet from base to point, shimmered in translucent gold. When he finally arrived, Dr. Robertson suggested it was a doorway and tossed a stone through the center. Ripples fanned out in the golden sheen, but the stone never landed on the other side. Suddenly, Dr. Robertson jumped in himself, larger ripples this time. Moments later, the rock landed on the far side of the portal, smoking and scorched. We waited.