I like the Twin Falls hike. It is only about 4.5 miles long but there is plenty of elevation gain and the river (South Fork of the Snoqualmie River) and falls both sound and look spectacular.
There are, of course, two waterfalls at Twin Falls, the upper falls and the lower falls. The view above, taken from the first view point on the hike, shows both of them from a distance of about .5 miles.
At 1.3 miles you reach a bridge that crosses the river just above the top of the lower falls. Here is a view looking up and a view looking down:
And, to top it off, there is a nice view point (going down from the trail about 100 steps) of the lower falls:
So whaddya think? Is this a fun hike or what?