Cougar Hot Springs, Hot spring in Willamette National Forest, Oregon, US.

Cougar Hot Springs, also called Terwilliger Hot Springs, is a set of four soaking pools built from river stones on a hillside in the Willamette National Forest, 53 miles east of Eugene. The pools measure 3 to 12 feet across and 2 to 3 feet deep, with exposed bedrock, gravel, sand and debris on their bottoms. Water flows from a rock face above the topmost pool at about 112 °F and cools to 85 °F in the lowest pool, draining into Rider Creek.

In the 1860s Hiram Terwilliger filed a cinnabar mining claim and then promoted the springs for mineral-water balneotherapy, though the Forest Service refused his request for mineral rights. Paving of local roads in the 1960s brought crowds between 1960 and 1990. Volunteers led by a Eugene stonemason rebuilt the pools in 2009 with natural mortar at a cost of about $40,000.

Bathing without clothing is permitted in the pools, but nudity is not allowed within sight of the Aufderheide Scenic Byway (Forest Road 19). The Forest Service banned alcohol and night use in 1998, and the nonprofit Friends of the Springs has provided a caretaker who maintains the trails and toilets.

The pools lie about a quarter mile from Forest Service Road 19 (Aufderheide Memorial Drive), 53 miles east of Eugene. Access carries a day-use fee, and the springs are open for day use only; alcohol, pets and overnight camping are not allowed. Clothing is optional in the bathing areas, but nudity is not permitted within viewing distance of the road.

The springs flow from a rock face at about 112 °F (44 °C) above the topmost pool, while the lowest pool is 85 °F (29 °C). The pools were rebuilt in 2009 by volunteers led by a Eugene stonemason, who removed concrete and used natural mortar; the work cost an estimated $40,000.