Imnaha offers a magnificently beautiful bike climb on a gravel road into Hells Canyon Recreation Area. The road is in good shape, albeit narrow and not recommended for trailers, but who cares when you are on the narrow tires of a cylocross bike. The road eventually terminates near the Hat Point Lookout, so don't worry about trying to make a loop of it unless you're on a mountain bike. You can also ignore the warnings to stop and cool your brakes on the way down.
The gradient is consistent at around 10 percent the entire way, as you weave through a canyon along Deer Creek shortly into the climb. After passing the Entering Hells Canyon Recreation Area sign (at the Deer Creek Trailhead), the road bends around and eventually arrives at the Five Mile Overlook. Here you start to see the rugged terrain of the Hells Canyon area with a backdrop of the Wallowa Mountains. The climb borders on epic from here, as it hugs the steep walls of the canyon on a narrow cut of road. Eventually it begins to top out near Buck Point, although there is no distinct point in the road for this so feel free to turn around or explore more from there.
One problem with Hell is that it is Hell. Firstly, there are goatheads. Secondly, it is hot as Hell in the summer. Thirdly, there are rattlesnakes everywhere. So, this climb is best attempted in the spring just after snow melt, while the goatheads are in their infancy, the snakes are hiding out, and the hills are green.