All-day trek takes the best trails at two great parks along Skyline Boulevard southwest of Silicon Valley. This is a great route for expert hikers -- it starts out in the lush redwoods of Sanborn Skyline County Park southwest of San Jose, climbs to Skyline Boulevard (Highway 35) and crosses over to Castle Rock State Park, where it takes the popular Saratoga Gap Trail and returns to Sanborn Skyline. Note this is very strenuous outing -- 16 miles with over 3,000 feet of elevation gain -- but could be an excellent training hike for High Sierra adventures like Yosemite's Half Dome. The views of the Santa Cruz Mountains are awesome at Castle Rock. On your way back, check out Indian Rock, just off the Skyline Trail -- it's one of many fascinating formations along this route. Trails on this hike: First leg from Sanborn Skyline: Sanborn Trail to the top of the ridge near Highway 35. > Skyline Trail till you see the crossing to Castle Rock State Park. Second leg from Castle Rock: Saratoga Gap Trail to Trail Camp > Service Road to Loughry Woods Trail > Cross Highway 35 Third leg: Skyline Trail back to Sanborn Trail > San Andreas Trail back to the parking lot at Sanborn Skyline Park.