Grab a mountain bike and take the Iron Horse trail.

http://www.parks.wa.gov/parkpage.asp...k=Iron%20Horse

Only issue will be the tunnels in the upper Yakima River Canyon between Cle-Elum and Thorp (they are closed), the other closed tunnels are easy to get around.

East of Kittatas you'll need a permit from the DNR, but they are easy to get, and they will send you a series of maps that highlight go-arounds for closed bridges in eastern washington.