I think it would be super fun to stay in Sisters or Sunriver and enjoy some of the Scenic Bikeways of Central Oregon. The first on the list is McKenzie Pass, 38 miles one-way, which I think would be best enjoyed as the first ride of the adventure.
Sisters to Smith Rock might pose as a fun add on to a one-way McKenzie Pass ride, or a fun loop on it’s own right. Twin Bridges Loop is 36 miles total and makes for a perfect day trip. Madras Mountain Loop is also another perfect 29-mile day trip. Can’t go wrong!
There is also Crooked River Canyon, a 36-mile round trip scenic ride that would be fun as a day trip.