When Bertha, the world’s largest tunnel-boring machine, stalled below the Seattle waterfront in 2013, the entire city was thrown into suspense as to whether the new Highway 99 Tunnel under what was once the Alaskan Way Viaduct would ever see the light of day. But the 53 1/3-foot-diameter tube, two miles from Sodo to South Lake Union, finally opened triumphantly in 2019.

Learn – and see, though spectacular photos by Catherine Bassetti, the project’s official photographer – how the massive Supertunnel project that changed the face of Seattle’s waterfront forever was conceived, constructed, and completed. She will be joined by Brian Russell, the projects lead engineer.