Highway 21 is a cross-border spur in the Regional District of Central Kootenay in British Columbia. First opened in 1964, the highway travels 14 km (9 mi) northwest along the Kootenay River from its connection with Idaho State Highway 1 at the Rykerts Canada-U.S. border crossing to a point on the Crowsnest Highway (Highway 3) just 1 km (about ½ mi) west of Creston.