There's beautiful scenery up the East Fork of the Lewis River, and campgrounds at Sunset Falls (CycleWild rode
there this year) and Rock Creek. The road is a little narrow with some faster traffic, so here's a 2.5 mile stretch where you can have a little break and a peaceful, relaxed ride. It's a Clark County multi-use path (hikers, horses, bikes all OK).
About 1/4 mile east of Lucia Falls County Park, turn off the Lucia Falls Road onto Hantwick Road, cross the Lewis River and pick up the trail in about 1/4 mile, immediately after the road crosses the railroad track. It's not marked but it is obvious; a paved path with bollard. The parking lot is up the road another couple hundred yards but it's steep so the trail is a better way to get there, even if you want to use the porta potties in the parking lot.
The first ~0.7 miles of the path is paved, the next 1.8 is hard-packed, small-crushed gravel over a well-built bed (1/2" minus in fine-grained matrix, not loose!). Skinny-tire riders use your judgement (I suspect you'll be OK) but most touring rigs won't have any problem. All of it is at least 10 feet wide, well-graded and maintained free of bumps, ruts, mud and roots. No cross-streets or motorized traffic. There are nice views of the river, it's all forested (maple, alder, fir, a few cedar), and a couple streams have water (filter or treat it, of course). There are picnic tables at the end of the paving and again near the Moulton Falls bridge at the east end, and a bench overlooking the river in the middle.
On this Google map
, "P" is the parking lot on Hantwick Road, and the purple trail is the bike-accessible path. The Bell's Mountain trail in blue is open to bikes but is steep single-track, not part of my suggestion for an easy bypass for touring bikes.