The trail out of Canyonlands National Park. It leaves the park eventually, and travels through many miles of BLM land, where there are ancient ruins, cliff dwellings and rock art, and incredable other worldl like scenery. Ive done it on my dirt bike several times, and in a rented jeep once. It's at least a 2 day trip, maybe 3, one way. It's filled with rock ledges, boulders, sand, off camber climbs and descents, awe inspiring vistas, and enough challenges to keep any driver on their toes. It's like being on Mars I imagine, but with air.
2nd would have to be New Jersey's Pinelands National Reserve. 1,000,000 acres of Beautiful scenery, many, many miles of trails, enough mud to swallow a tank if that's what your into, lot's of historic sites, it's close and what I got here. OH, and it's FREE.