There are two routes to the Green Lakes. The northern is closest to Sisters, OR. The most scenic route is from the south, starting off FS 46, west of Mt. Bachelor ski area. Says SierraHiker
There is only one trailhead, so in and out is the way to backcountry trek it normally. This is a wilderness hiking trail that is quite long, so do pack enough food to last the whole trip. The time needed for this backcountry trek is roughly 7.5 hours, but you never know stuff could go wrong and you could get stuck so be prepared for that. With its 8.2 miles of walking distance it's a mid length hike. There's not much difference in elevation along the hiking and backpacking trail which means the conditions are about the same from start to finish. The total elevation difference for Green Lakes Trail is 929 feet which is a lower than average number.