Milepost 31

Deep below the streets of Seattle, a giant tunneling machine is digging a tunnel to replace the Alaskan Way Viaduct, an elevated highway that has spanned Seattle’s waterfront for over 60 years. Milepost 31, the SR 99 Tunnel Project’s information center in Pioneer Square, provides an inside look at this massive project and highlights the history of the Pioneer Square neighborhood.

Explore how Seattle’s landscape has changed during the past 20,000 years through soil samples and interactive displays. Discover tunneling equipment and the 10-foot-long model of Bertha, the nation's largest tunneling machine. Witness history in the making as this project – along with the Elliott Bay Seawall Replacement and Waterfront Seattle – transforms the future of Pioneer Square and Seattle’s waterfront.

Milepost 31 offers a variety of programs for visitors of all ages. Free guided viewing platform tours allow visitors to get an up-close look at the SR 99 tunnel’s south portal construction site. During the summer, a free public bike tour that follows Bertha’s tunnel route provides a unique way of understanding the historical and engineering aspects of the project. Hands-on activities introduce school and youth groups to engineering and how this innovative machine digs a tunnel.

During the First Thursday Pioneer Square Art Walk, Milepost 31 hosts a speaker series from 6-6:30 p.m., giving visitors further insight into this huge engineering project and the geology and history of the neighborhood.

Please come visit this free exhibit. We promise you won’t be bored!

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