Distance (round trip): 9.4 mi.
Elevation Gain: 1,390 ft.
Beginning at the Glacier Gorge Trailhead, Black Lake is 2.2 miles further along the same trail as Mills Lake. Passing Jewel Lake is an unusually marshy trail for Colorado, but you can avoid getting muddy thanks to the plethora of boardwalks built into the trail.
Because it is mostly uphill with lots of stairs, the trail to Black Lake can seem longer than the additional 2.2 miles from Mills Lake. However, the trickling streams and waterfalls along the way make it a worthwhile venture. Black Lake itself is an intriguing, dark color and lies under McHenrys Peak.
If you choose to go even higher, Blue Lake and Green Lake are both in this same basin.