The Gorkha Museum occupies a building near the lower Durbar area and focuses on the history of the Shah dynasty and the rise of unified Nepal. Exhibits cover the military campaigns of Prithvi Narayan Shah, the royal genealogy, traditional weapons, ceremonial dress, and everyday objects from the palace household. Signage is in Nepali and English, though the English translations vary in quality.
For visitors already interested in Nepali history, the museum adds useful context to what you see at the Durbar above. For others, a quick walk-through — half an hour or so — is sufficient before heading up the hill. Entry is inexpensive.