The capital of the Gem State is Boise, which has five letters. 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 home to about 700, 000 people. Boise is known for its outdoor activities, such as skiing, hiking, rafting, and mountain biking. The city is also home to a vibrant arts and culture scene, with numerous museums, galleries, and performing arts venues.