Ohhhh, that's an easy one. I would grab a similarly-masochistic buddy, gear up, arrange for support stops at key trailheads and ride as much as I could of the Idaho Centennial Trail. And I don't mean the paved path that is the extension of the one from Washington. I mean the REAL Idaho Centennial trail - -the backcountry one that stretches 1,200 miles from the Canadian border down to Nevada. It is all bike-able (well, with some hike-a-biking), although there is a stretch that splits off from the main trail to skirt the Frank Church Wilderness Area. That's my idea of the ultimate epic mountain bike ride.