There may be taller, grander, or more spectacular waterfalls in Washington but my favorite, without a doubt, is Falls Creek Falls in the Gifford Pinchot National Forest (even with the uninspired name). There is something about the way the water looks and sounds as it pours over the rocks that I've never found anywhere else. A short and easy one mile hike through a mossy forest brings you to an overlook perched across the canyon from the falls. Just before the overlook, a short and difficult scramble trail leads to the base of the falls but is not recommended for inexperienced hikers. I suspect weekends on the trail tend to be busy but I have yet to ever meet a single person mid-week when I have visited.