Jaca's large, star-shaped citadel, built in the 1590s to defend against possible French invasion, is surrounded by an equally star-shaped moat inhabited by a herd of deer. Inside, you can explore the bastions, casemates, powder magazines and chapel as well as the broad central Patio de Armas.
The citadel also hosts the surprisingly good Museo de Miniaturas Militares (www.museominiaturasjaca.es), a model soldier museum with detailed battle scenes providing a visual military history lesson from Hannibal's elephants to Franco's fascist tanks.