Quite an amazing place, a mix of military museum, ornate palace and tribute to one of Portugal's poets Luis de Comoes (Tripadvisor link) It's situated in the old arsenal and spread out over two floors, be careful about the route you follow as once up the stairs you need to visit the Napoleonic and WW1 collection before heading into the medieval/renaissance armour or you'll end up having to retrace your steps like we did. Many of the elaborate rooms with arms and armour are very dimly lit and flash photography is not allowed.
This photo of Museu Nacional Militar is courtesy of TripAdvisor
To start downstairs, lots of ancient cannon and an amazing ceiling
Intersted in headgear then this is the room for you
Plenty of models of artillery
Interrsted in the ECW or TYW then this is an interesting period when Portugal fought for its independence from Spain.
The room dedicated to Luis de Comoes.
WW1 quite a few dramatic models and pictures
Back downstairs, yet more cannon.
I couldn't take any pictures because cars were in the way, but the central courtyard is surrounded by pictures of Portuguese battle in blue tiles.
Was it worth 3 Euros - definitely