Slate Peak to Robinson Pass is a 6.3 mile lightly trafficked out and back trail located near Mazama, WA that features a river and is rated as moderate. The trail offers a number of activity options and is accessible from May until October.
It's 4 mile out and back if you park 2 miles from the lookout tower, but you can also drive to well within a 1/2 mile. Because it it such a short walk I only gave it 4 stars, but the 360% view of the surrounding peaks and valleys is pretty amazing. I recommend hiking along the PCT while you are up there or one of the other well marked trails.