The south portion of the Interurban Trail provides a nice, flat urban walk or bike ride on a paved trail beginning in Fort Dent Park in Tukwila through Kent, all the way down through Auburn and beyond. Buildings, streets, and railway lines are visible for the entire length of the trail, but the further south you venture, the more scenic the trail becomes.
Historically, this was the route of the Puget Sound Electric Railway, which provided a trolley between Tacoma and Seattle but falling out of favor after the advent of personal cars. Today, it's only possible to walk or ride as far as Pacific.
In Fort Dent Park, follow the River Trail signs, link up the Interurban Trail, and cross a bridge over the Green River before arriving at a BNSF train yard. Passing through the yard, you'll cross the tracks twice. Be careful crossing as some the locomotives are remote controlled. You may also have to wait for the trains to stop or to clear the trail.
On clear days, as you head out of the railyard and further south, you may be able to spot Mount Rainier as you pass through Kent. Here, the Interurban Trail links up with the Green River Trail, which you can hop on to loop back 11 miles north to Fort Dent.
If you choose to continue on, you'll soon enter a more agricultural area, with farmland and more views of Mount Rainier, as well as Emerald Downs, a racetrack located just outside of Auburn. Continue south through the smaller towns of Algona to where the trail ends in the town of Pacific.