More than a single, uniform wall, Cartagena is surrounded by a series of impressive fortresses, most of which are still standing. The largest and most important was Castillo de San Felipe de Barajas, a towering stone fort just east of the walled city along Avenida Pedro de Heredia. The sacking of the city by Sir Frances Drake highlighted the need for protection, and so this mighty fort was built between 1656 and 1798 with plans from a Dutch engineer. The fort is an ideal spot from which to watch the sunset, and getting the audioguide is well worth it, as you can walk around the fort walls and underground passages at your leisure, learning about its history, functions and other important landmarks, such as the leper hospital. Alternatively, you can talk to one of the guides who hang around at the entrance.