United States Army Museum of Hawaii

Tucked right in Waikiki at 2131 Kalia Road, this museum covers Hawaii's deep military history from the ancient Hawaiian warrior era through modern conflicts in the Pacific — and it's completely free to enter. Housed in a historic coastal artillery battery, the exhibits include weapons, uniforms, vehicles, and stories spanning World War II, Korea, Vietnam, and beyond. It's a surprisingly absorbing stop that most people walk right past on their way to the beach.