Cascade Rock used to be accessible from the backyard of many sites at the Elwha Campground, but with the removal of the Elwha Dam, this campground has flooded multiple times and the campground is closed. Luckily though, you can still hike Cascade Rock, and its such a secret trail, you're likely to have it to yourself.
Begin from the paved parking area off the Olympic Hot Springs Road, about 50 yards past the one-lane bridge. Cross the road, and enter the former Elwha Campground. Head for the river at the back of the campground (you'll be able to hear it), passing a large day-use picnicking area on your left.
You'll need to ford the creek to access the trail. In late summer and fall, it will be running low enough to cross safely, but evaluate it carefully in spring -- high water can be dangerous.
Once across the water, follow temporary signs for the Elwha Valley Access Trail. The large yellow arrows mark your path. Hike away from the creek, then jog left at a sign with an arrow for both the access trail and the nature loop.
Begin climbing, passing a few boggy spots before finally getting out of the muck. Large maple leaves litter the ground year round, but especially in fall. Step carefully, at this time of year they can be slippery! At 0.2 miles a turnoff for a viewpoint is to your right. It's worth the side trip, as it's the best view you'll get on this trail.
Back on the main trail, about a half mile from the campground, arrive at another junction where a trail joins up from your left. This is an alternate access route for the Cascade Rock trail, but it comes from a much smaller, unmarked parking area just off the Olympic Hot Springs Road.
Continue climbing. The trail is quite steep for a short bit before becoming a much more gentle traverse. The sound of the rushing Elwha fades away and a deep silence comes over the area. The trail is fading from lack of use since the campground has been closed, and knee-deep salal crowds the tread, but it alternates with some sections that are wide open, complete with red, peeling madrona trees.
Traverse for another mile, climbing steadily but gently, until the trail comes around a ridge just south of a saddle visible through the trees. To the north is Madison Creek's drainage. Once more, the trail begins climbing more aggressively. It's just another 0.3 miles but you'll gain 300 feet of elevation.
The summit isn't much, just an open, mossy bit of granite, but the silence is absolute up there, broken only by birdcall. Take a minute. Listen to your breath (or look at it, if it's cold enough) before making your way back the way you came.