Unbelievable views and not a ton of elevation gain make this a truly amazing ride that should take about 2-3 hours one-way.
Starting in the "Old West" town of Sisters, Oregon and ending at Smith Rock State Park outside the small town of Terrebonne, this route takes riders past a variety of historical sites, shows the gentle curves of the Deschutes River and frames spectacular views of the Cascade Mountains, and ends with the dramatic walls of Smith Rock State Park.
You can plan to do this in two hours one-way if you don't stop and keep your head down, but I would recommend making this a casual day since the route is quite scenic. Traffic is minimal for most of the route, except for an ~0.1 mile stretch along Highway 126 outside of Sisters and a crossing of Highway 97 in Terrebonne. The outbound trip to Smith Rock is net downhill, with minimal elevation change except for a climb into Terrebonne proper. There are almost no stores or gas stations in between Sisters and Terrebonne, and no bike shops anywhere outside Sisters, so be sure to bring plenty of food, water, and spare tubes.
If you make it a round-trip ride, stop in for lunch at Sandbaggers Saloon in Terrebonne (technically at Crooked River Ranch, just off the route) for a little baked Mac N' Cheese or Base Camp Pizza (just on the Smith Rock side of route 97). And, when you get back to Sisters, be sure to treat yourself at the Sisters Bakery before heading to any of the town's many saloons.