The city walls, a mixture of red limestone, granite and brick, were built under Alfonso VI, following his capture of the city from the Moors in 1090; they took his Muslim prisoners nine years to construct. At closer quarters, they prove a bit of a facade, as the old city within is sparsely populated, most of modern life having moved into the new developments outside the fortifications. It’s possible to walk along two sections of the walls from Puerta de Carnicerías to Puerta del Carmen and from Puerta del Alcázar to Puerta del Rastro; the former being the best with some stunning views of the town. There have been some experiments with night-time opening in the summer (usually 10pm–12.30am Sun–Wed), but check with the tourist office. Tickets are available from the green kiosk by the Puerta del Alcázar and the tourist office at Puerta de Carnicerías.