This hike begins from the Wild Basin Trailhead, which is located South of Estes Park and about 15 miles from the main entrance to Rocky Mountain National Park. The roads are well-paved until the final 2.2 miles, which is on a gravel road. While the main attraction is the final destination of Bluebird Lake, you will also pass many sights, including Copeland Falls, Calypso Cascades, Ouzel Falls and Ouzel Lake. Ouzel Lake is the only one that you will have to divert from the main trail in order to see, which is clearly-marked with signage.
Backcountry campsites are available as well, all of which are easy to follow through the trail signs. It is a busy trail in the beginning stages of the hike, but once you pass Ouzel Falls, the crowds thin. As you approach Bluebird Lake, there are some large snow fields lingering as late as July. With good hiking shoes, you'll be fine crossing them. If you do this hike in the spring, you may want to speak with a ranger regarding the snow level.
The first attraction you will reach comes quickly in Copeland Falls, in which there is an upper and lower section. From that point, proceed to Calypso Cascades, though the trail does take you over a bridge to get across an unnamed waterfall as well. Though unnamed, it's still worth a pause to take in the view. From Calypso Cascades, it is another mile to reach Ouzel Falls. While you're able to see a beautiful view of the falls from the trail and the bridge that overpasses Ouzel Creek, you will want to veer off the trail a short distance to get a view of the top of the falls. The trail starts right before the bridge and continues up the side of the waterfall until reaching the viewpoint for the top of the falls.
From Ouzel Falls it is about 4 miles to Thunder Lake, mostly hiking through dense forests with the occasional meadow and a few creek crossings. You'll have a few lookouts with gorgeous views along the way and pass a few small ponds as well, but nothing compares to the main attraction. This trail will also take you to the Lion Lakes offshoot, which is a couple of miles farther. Upon reaching the lake, which you're able to fish in, you'll notice the snowmelt makes the surrounding area a little swampy. Waterproof hiking shoes or boots will come in handy. The lake is framed by Tanima Peak to the south, and Pilot Mountain and Mount Alice to the northwest. Make sure to allot time to sit and enjoy the beautiful views.