With a thick and highly variable mixture of glacial and nonglacial soils overlying bedrock, punctuated by seismically active fault zones, Seattle is a challenging arena for geologists, engineering geologists, and geotechnical engineers. Because of this geologically complex stratigraphy, Seattle has a higher density of geoprofessionals and subsurface explorations than other cities of equal size. Even so, the subsurface always delivers surprises when construction begins. By visiting three major civil works, SR 520 floating bridge, Alaskan Way Viaduct/SR 99 tunnel, and the Beacon Hill Transit tunnel, you will discover the interaction between Seattle geology and the engineering that made these projects successful.