Despite the name, this excellent museum is far more than just a display of military hardware. The collection is housed in Bayt al Falaj, built in 1845 as a royal summer home but used mostly as the headquarters of the sultan’s armed forces. The lower rooms outline Oman’s history while the upper rooms explore the country's international relations and military prowess. The museum is on the itinerary of visiting dignitaries and you’ll be given a mandatory military escort.
If you haven't time to visit the mountains to see Oman's ancient engineering in action, there’s a working model falaj (irrigation channel) in the grounds outside the museum that is worth a look.
