One of my favorite biking trails is the Trolley Trail on the outskirts of Spokane, WA. It starts out like a smooth riding roller coaster with about a dozen humps. The trail surface starts out as fairly hard packed soil with pine needles to cushion your ride. The old trolley line with rails removed turns a bit rocky in places, going down hill with only a slight decline. About 1 1/2 miles in it opens up a mostly barren hillside and a 60 foot quick rocky drop (which I can handle now with my hydraulic brakes).
At this halfway point it rises and goes into a tree covered smooth trail again with occasional Deer, marmot and Moose sightings. Then it passes in a completely tree branch covered portion where several wooden boards were laid in what becomes mud in heavy rain, it is possible to walk your bike through this area that is only about 40 feet long. Then the trail has panoramic views of the City of Spokane in the distance and a highway down in the valley.
To this point a Mountain bike isn't really necessary except for the afore mentioned quick 60 foot drop. Now the trail turns downhill with medium sized rocks about 5-8 inches across and 3 - 7 inches high to avoid, again my hydraulic brakes make this part of the trail manageable again. Then the trail moves more parallel (horizontal) to the hill and is actually not part of the Official City/County owned Trolley trail. Just before the unofficial end of the Trail it goes straight downhill on a firm gravel surface to a low traffic city street which is only a few blocks from the large paved 'Rails to Trails' Spokane to Cheney Trail which is 15 miles long and almost all paved with water fountains, large paved parking lot, and restrooms at both the Spokane and Cheney ends of the Trail.