The Greek island of Keros is a mountainous protrusion from the Aegean Sea. Around 4,000 years ago, humans carved the cone-shaped land into terraces to resemble a stepped pyramid.To make it gleam in the sunlight, it was clad with a thousand tons of imported white stone. The pyramid itself is nothing new. But in 2018, researchers found a surprise when they looked inside—a sophisticated system of drainage tunnels. It dated a full millennium before the advent of the remarkable plumbing of Crete’s Minoan palace of Knossos.Discovered while excavating a large outer staircase, the system’s exact purpose still needs to be determined. The pyramid’s plumbing could have funneled fresh water or removed sewage.Keros became a major ritual center in the third millennium BC. The community that built and maintained the sanctuary populated the nearby island of Dhaskalio.The settlement was exceptional in several ways. Even though Dhaskalio was the region’s most densely settled island and everything from food to material had to be imported, they aced the considerable effort needed to keep the site going. Newly discovered workshops also proved the excellent metalworking craftsmanship during a time when such skills were basic and rare.