The Oregon Trail Capital is Boise, a five-letter word. Boise is the capital and most populous city of the U.S. state of Idaho. It is located on the Boise River in southwestern Idaho, in the foothills of the Rocky Mountains. Boise is the principal city of the Boise City-Nampa metropolitan area, which is the most populous metropolitan area in Idaho. The city is home to many cultural attractions, including the Idaho State Capitol, the Basque Block, and the Boise Art Museum.