This is an epic hike & bike combining the classic bike ride up to the mountains and back (either on the rode or MTB trails) with a summer summit of South Sister. I've only done half of it, staring at the trailhead near Devil's Lake, summiting, descending, and then biking home. The full leg-melting adventure would start on bike in Bend at roughly 3,600 feet and climb fully self-powered up to South Sister's summit at 10,358 feet. Oh, and there's fishing too!
South Sister is really popular with hikers because you can reach the summit via an entirely non-technical trail. Even in early fall snow tough hikers can still make the top without any climbing equipment or gear. This means you get the mountaintop experience without the usual prerequisite mountaineering work. It's even popular in early summer when the highway first opens for backcountry skiers and split-boarders to hike the summit and then ride down. To make a great thing even better, why not also spice it up with some biking and fishing?
To do so, I climbed the mountain via the main trail that starts across the highway from Devil's Lake. But then on the way back down I broke off on an unofficial and unmaintained "trail" that drops off the east side of the mountain down to Green Lakes. This allows for fishing at Green Lakes as well as Fall Creek, which flows alongside the trail down from Green Lakes to the highway. It also means you get to cover more ground and see different terrain on each leg of the trip. Both routes are beautiful, though the scree trail from Green Lakes to the summit is tough anytime and was somewhat agonizing to descend in the snowy late September conditions. I basically tried to glissade as much as possible up high, but further down the snow was too soft and I punched through into jagged lava rock multiple times. So, I only recommend the Green Lake route in peak summer conditions.
If you're looking for an overnight adventure, you can camp on the summit and (weather permitting) enjoy a cold but brilliant night of stargazing. Otherwise, take a break for lunch with a view and then get your knees ready to hike down to do a bit of fishing in. Note: Bring a jacket because it's usually windy and cold on top.
There's a good chance you'll get to watch the California Tortoiseshell butterflies putting on a dazzling mountaintop display.
The way I did it is I hitched a ride up the mountain and stopped along the way to lock my bike at the Green Lakes trailhead. Then I got dropped off further up at the climber's trailhead with my hiking gear, fishing stuff, and food. So I ended my mountaineering adventure at my bike and then rode down to town. For the most fun, ride the MTB trails down. If your legs are shot though, you can always take the highway. Don't forget that there is a decent climb back up to Mt. Bachelor before the true downhill begins.
See my Strava here. Note that even without biking up the mountain, it was nearly 7,000 feet of climbing. This really is a super big day. Biking there first would make it meteoric.