Along with several other wonderful trails, the hike to Long Lake, Lake Isabelle, and Pawnee Pass starts at Brainard Lake Recreation Area just an hour's drive from Boulder. At 9 miles round-trip with just over 2,000 feet in elevation gain, this is a moderate hike that passes through subalpine forests, alpine lakes, and offers fantastic views of the Indian Peaks and the tundra above the tree line.
Starting at Brainard Lake, there are plenty of opportunities to see wildlife, especially given the healthy population of moose in the area. While there is a parking lot at the Long Lake Trailhead, it is very small; it is best to arrive well before 7 a.m., especially on weekends. If this lot is full, there is usually plenty of space in the day use parking area at Brainard Lake, though that adds about a mile each way to the hike.
Long Lake is only a quarter of a mile away on an easy hike with little elevation gain. Once there, take a moment to enjoy the view from the bridge over the South Saint Vrain Creek on the east end of the lake. The trail continues through subalpine forest as it proceeds into the Indian Peaks Wilderness, and Lake Isabelle is almost 2 miles ahead. Wildflowers around streams and around the lake add color to the beautiful views of the Indian Peaks in the background, most notably Navajo, Apache and Shoshoni Peaks, with Navajo Glacier being visible from the trail. Note that the lake is in the Boulder watershed, so it is often drained in late summer to feed Lefthand Reservoir.
After Lake Isabelle the trail is rockier and steeper, but the views make the hike well worth it. As the trail zigzags through the rocky outcrops it offers wonderful views of the lakes to the east and Indian Peaks to the west. Above the tree line, take time to look at the micro-scale forest on the tundra.
Pawnee Pass, on the continental divide, is 12,550 feet above sea level and marks the border between the Roosevelt and Arapaho National Forests. From that point you can see Lake Granby some 8 miles away, and you can continue the hike north to 12,943-foot Pawnee Peak or west to Crater Lake.
Note that the gate at the fee station is generally open from Memorial Day until sometime in October, depending on weather conditions. If the gate is closed, it is possible to hike or bike 2.5 miles to Brainard Lake.