The Middle Sister, the lowest of the Three Sisters, offers a great alpine experience for novice mountaineers and rewarding, panoramic views of the surrounding Cascade. There are several routes to the summit; from the east side, the mountain is accessed via the Pole Creek Trailhead using a route that leads over Hayden Glacier.
Pole Creek Trailhead was the origin of a large forest fire back in 2012, and it is still a sensitive area. This approach winds through a large section of this burn where plants are slowly recovering and there is little shade. The climber's access trail is no longer marked from the main trail, and it is difficult to follow once you are above timberline. Should you miss the turnoff nicknamed the "sandy split," stop at the crossing of North Fork of Whychus Creek and follow the creek up toward the glacier.
For those familiar and comfortable with glacier travel, Hayden Glacier offers the quickest, most direct route up the mountain. For others who would rather skirt the glacier, follow the North Sister route up to the top of Collier Glacier, then transverse around Prouty Point and onto the saddle where Hayden Glacier and Renfrew Glacier meet. From there you'll have to scramble up loose rocks and scree to the summit.
The conditions on this route vary greatly depending on the time of year you decide to summit. Snow can linger on the steeper top section of the mountain as late as mid-August, making crampons and an ice ax a necessity. From late August until early October the summit is normally clear, and a summit can be completed without the crampons and ice ax. However, the last steep section of the Middle Sister is composed of very unstable rock, and the scramble up to the top can be fairly precarious. Take your time and mind your footing. Be aware of people below you, as it is easy to dislodge rocks as you make your way up.
Several backcountry campsites dot the area should you want to camp. Campfires are not allowed within 100 feet of water or the trail. Remember to "Leave No Trace" when traveling through this area.