Starting from Castle Pass, and the crowded junction of the PCT, start right up the west ridge of Castle Peak. Trees diminish and the views get grand, both of this peak and the entire region. A steep and rocky scramble gets you to the final summit, with 360-degree views. On clear days, you can see Mount Diablo in the bay area, the snow-covered Lassen Peak way to the north, and all the mountains that ring Lake Tahoe.
Once you've taken in the splendor offered by the summit, head back the way you came to reach the intersection with the Hole In The Ground Trail
, or the PCT: Highway 80 to Highway 49 (near Sierra City)