Terwilliger Hot Springs, also called Cougar Hot Springs, is a developed group of four geothermal pools in Oregon’s Willamette National Forest, built up from river stones on a hillside above Rider Creek. Long possibly used by Indigenous peoples, the springs were established for mineral-water bathing by Hiram Terwilliger in the 1860s. Paved roads in the 1960s greatly increased access and helped make the site a major public destination in the western Cascades, but popularity also brought crime, vandalism, and stricter Forest Service controls. Volunteers renovated the pools in 2009, and after damage from a landslide and fire, the springs reopened in 2019 as a fee-based day-use site.