Thousand Island Lake is one of the popular transit points on the John Muir Trail. It is also popular among 1-2 night backpacking hikers as well. You can get to the lake either from Agnew Meadows or from Rush Creek. Both are really hard hikes to do as a day hike, but there are folks who do it. Of course, when you do it as a day hike, you can’t catch sunrise or sunset (unless you like hiking in the dark).
Banner Peak and Mt. Ritter are magnificent peaks that you can see from a distance. When we hiked the JMT south bound, we saw the peaks for nearly 50 miles towards the South.
Thousand Island lake is at nearly 10,000 feet elevation and it can get windy up there. During our first night there, we perched our tents in an exposed area since we had great views of the peaks at night and suffered when winds kicked up for the night. There are sheltered areas, but alas without the magnificent views.
Thousand Island Lake has become one of my happy places in California and world wide. If you are a strong day hiker, you can see it in a day, but it is highly recommended if you can stay a night there to experience the lake and the peaks.