Milepost 31

Interested in learning more about the SR 99 Tunnel Project? Milepost 31 is an award winning information center that provides visitors with an inside look of the massive boring (tunneling) project that is going on right below downtown Seattle. Here you will learn about the history of the land and the importance of this reconstructed route and see model of the world’s largest tunneling machine, Bertha, and the opportunity to learn about planning and construction for this project as well as history of tunneling technology. 

The center also offers free public tours to exclusively see the SR 99 tunnel construction on the actual grounds and gain a better understanding of the history of tunneling technology.

211 First Ave. S

Seattle, WA 98104

(206) 995-8448


Tues | 5:30pm-6:30 pm
Wed-Fri | 12:00pm-1:00pm
Saturday | 12:00pm-1:00pm
               & 3:00pm- 4:00pm