Boat Box Hot Spring, also called Elkhorn Hot Spring, is a small soaking site on the Salmon River in the Sawtooth National Forest near Stanley, Idaho. Unlike larger developed springs, it consists of a single metal tub at the river’s edge, fed by hot spring water through a tube in the bank. Named for an earlier wooden tub lost to repeated flooding, it offers a very hot soak in a cramped space for only a few people. Easy roadside access, year-round use, and the striking contrast between hot mineral water, the cold river, and the surrounding mountain landscape give the site its distinctive appeal.