The Twin Sisters is one of a half dozen or so "classic" summit hikes in Rocky Mountain National Park; it is actually on the South-East border and crosses back and forth between
Roosevelt National Forest as well. On the web you will find it described as everything from "easy" to "strenuous"; I suppose it depends on experience and physical condition.
With it's 7.4 mile round trip and 2400 ft elevation gain, I will rate it as "moderately strenuous". Who cares? It's awesome - just do it!
Take Rt. 36 North from Boulder, head West on Rt. 7 at Lyons, and follow the signs for Estes Park heading North. That Rt. 7 is a very scenic drive in itself; like many Colorado roads, the scenery actually presents a driving hazard! You will eventually come to Lily Lake on the left; immediately across the road is a parking lot, and a dirt road behind it leads up to the trailhead. You can park in the lot, or drive up the road and park, save a half mile off the hike.
The trail leaves the road heading east through a dense lodgepole pine forest. The trail surface is fairly smooth on the lower end and quite comfortable to hike, if a bit boring initially. This trail heads in and out of National Park lands as it winds south, then east through numerous switchbacks to timberline. There are very few views in this dense forest. A little over a mile up the trail the forest opens up briefly at a large clearing giving you great views of the east face of Longs Peak and Mount Meeker. As you climb higher, lodgepole pine gives way to englemann spruce and the trail surface becomes more rocky, as well as steeper.
The trail transitions from dense forest to an area of smaller, less densely populated trees. Here the trail travels through aspen and low growing spruce. You get spectacular views of Estes Park, Lake Estes, and the Mummy Range as you cross over to the North and East sides of the ridge. The last quarter to a half mile of the trail climbs up through the rocky slopes below the peaks. The trail ends in a saddle between the peaks. You can reach either summit easily from there. No excuse not to do them both! The summit offers great panoramic views that include the Great Plains and the Continental Divide, a stunning picture of Longs Peak, and many many other mountains. Many many.
The trailhead is a tad over 9000 feet asl; the summit(s) about 11,400. It took me a little over 3 hours to the saddle, a little over 2 hours to get back. It can be done in less time; I am slow taking all these pictures and notes.
||Just past the clearing, a huge rock wall reminds you
that you are climbing a mountain, not waltzing through
|When you see this at the turn of a switchback you are exactly 1000 feet
above the trailhead. You can actually scramble up it from behind,
but don't waste your time - keep going, 1400 feet to go yet,
and the views will be better.