We will do the easy part of this hike. It is a good one if you are new to snowshoeing.
The trail to Castle Peak is 6.5 miles round trip. To get to the actual summit for Castle Peak would likely require snowshoes and is rated hard. However, the first part of the trail is a gentle uphill slope ideal for cross country skis or snowshoes. The trail initially leads to a saddle below Castle Peak. There are excellent views from the saddle. When you reach the saddle you then follow the ridge east to Castle Peak. It is this section of the trail that would be considered hard. The elevation gain to the summit is 1800 feet, from 7200 to 9000 feet.