There is an almost unknown trail that starts at the West Seattle Bridge and follows the Duwamish waterway over to the First Avenue bridge. From there a route takes you through lightly used industrial streets in the South Park neighborhood to Cloverdale where you pick up a short segment of the trail agian before a short steep climb. A short distance (and one busy street crossing) puts you on East Marginal Way with no traffic. You take that right beside SR 599 until it ends at a trailhead at Rock Wier in Tukwila. From there the trail is better defined, winding along the river to Fort Dent park and a connection with the Interurban Trail.
Probably the hardest part of the trail is the start – on a busy four-lane road with lots of trucks. The City said that the link to get the existing start of the Duwamish Trail connected to the Alki Trail would be built in 2004. Click the 2006 link to see what they’re saying now.
Probably the best description of the trail (especially the part on streets in South Park) is from Driesbach.
Here’s a King County map showing the Duwamish Trail.