Five thousand years ago Redmond, Washington, was buried under 3,000 feet of ice. Today we occasionally see large boulders—glacial erratics—that were left in the wake of the retreating ice. For the new Redmond Central Connector park, we built our own Erratic. We salvaged 3,000 steel plates from the BNSF Railroad that once crossed the site; these form the cladding for the Erratic‘s skin. Motion detectors inside the glass fronts activate colored LED lights, delighting passersby with an interactive experience.