The Twin Sisters Peak hike offers great views of Rocky Mountain National Park. The trailhead is easy to access as it's located close to Estes Park, Colorado.
The trailhead starts close to 9,000 ft elevation. It continues at a gradual slope through the forest for a long way. The trail does not exit the tree line until close to the top, where there is a boulder field, of sorts (slightly over 11,000 ft). Don't worry, there is a nice trail all the way to the top. Once you get to the top, however, there is a giant rock you can scramble up for a better view.
Twin Sisters Trail is well-marked and is a good path. There is one section, however, where a rock slide took out the path. Now there is an alternate path. The forest is filled with pine trees and the smells along the trail are amazing. The pine trees range from large to small - the higher you get, the smaller they get. As the trail goes higher there are better and better views. As you look out you can see the Rockies in all their majesty. There is also a great view of Longs Peak once you are on the top.
Note: at the top, there is an electrical tower and a small shack.
The reason I ranked this as moderate is because it is fairly high altitude and a fair distance, with a few thousand feet of elevation gain. If you are a beginner but are in good shape physically, I would say you could take this trail on. The real attraction here is the view. It is one of my favorite day hikes just for the simple fact that it is a fun hike with a great view.