Hells Canyon's most spectacular scenery is perhaps along Snake River, following 25 miles of paved road (Idaho's Rte 454) toward Hells Canyon Dam; here dramatic canyon walls loom almost vertically. The road goes along the Idaho border but is accessed via the southern end of the Wallowa Mountain Loop, near Oxbow. Just past the dam the road ends at the Hells Canyon Visitors Center and boat launch.
Miles beyond here, the Snake drops 1300ft in elevation through wild scenery and equally wild rapids, and the area can only be accessed via jet boat or raft.
There's also a gravel road that goes along Snake River on the Oregon side, but it stops short of the dam. It accesses Bureau of Land Management (BLM) land, and some trailheads and rustic campgrounds. There's no bridge linking this gravel road to Rte 454 over the Snake.
There are several good hiking trails on the way to the dam; Allison Creek (on the Idaho side), about 4.5 miles round-trip, is an especially good one. Longer trails are possible; check with the Hells Canyon Visitors Center, from where there's also the mile-long Stud Creek hike downriver.