Skyline-to-the-Sea Trail, Hiking trail in Santa Cruz County, California

The Skyline-to-the-Sea Trail is a 29.5-mile (47.5 km) hiking route from Saratoga Gap, at the junction of SR 9 and Skyline Boulevard, down to Waddell Beach on the Pacific. It passes through Castle Rock State Park and Big Basin Redwoods State Park, following SR 9, SR 236 and Waddell Creek.

Planning began in 1968, and the Sempervirens Fund of the Sierra Club's Conservation Associates started the trail in 1969, when Boy Scouts joined a "trail breaking party" and volunteers cleared about 45 mi of paths. The route first ran along SR 9 from Saratoga Gap to Big Basin. The western end reached the Pacific at Waddell Beach in July 1978 after the Hoover Ranch and Rancho del Oso land was acquired.

The trail's name comes from its route between the Santa Cruz Mountains ridge and the Pacific. Its first segment was built in April 1969 during a "trail breaking party" that grew into annual Trail Days, when nearly 2,500 volunteers cleared and cut almost 45 mi (72 km) of trails. Boy Scouts took part in the original work.

This route requires careful planning for multi-day hikes with overnight stays at designated camps. Visitors should expect changing weather conditions and check multiple access points before setting out.

A 50 km ultramarathon runs the east-to-west route from Saratoga Gap once or twice a year, with 910 m of climbing and 1,790 m of descent; the 2020 course record stood at 3:40:43, set in 2016. Hikers starting at Castle Rock instead of Saratoga Gap add about 4.8 km via the Saratoga Gap and Travertine Springs trails.