Castle Peak, at 9,098 feet, is one of the most panoramic peaks in the North Lake Tahoe region. This is a wonderful hike, but due to the lack of shadows, the steepness of the hike, and the exposure to the Sun, the hike is best done in late season, in late September or October, when the Sun is less strong.
From the Highway 80 exit at Boreal / Castle Peak, take the road that goes North from the exit. The road soon turns into a dirt road, and you can park at the gate (a couple of hundred yards from the highway exit), or you can continue further, depending on the clearance of your vehicle and your confidence driving a rough dirt road.
Once parked, follow the trail keeping along, and left, of Castle Creek, until you arrive at Castle Pass. From there, follow the trail on the right, which leads directly to Castle Peak following the crest.
Castle Peak is composed of three peaks, and the highest is the most southern. Getting to the two southern peaks requires some scrambling on rock that is stable and full of foot and hand-holds. You can decide to visit only the easiest, northernmost peak, or scramble on top of the others as well: the view will be wonderful from all of them, ranging from Sierra Buttes to the North, South Lake Tahoe to the South, and — I am told — Mount Diablo to the South-West in very clear days!