One of the most fascinating places to visit in Cartagena is Castillo San Felipe de Barajas. It was originally built in 1536 and is the strongest fort ever constructed by the Spanish anywhere in the world. It's included in the UNESCO World Heritage listing for Cartagena.
Originally known as Castillo de San Lázaro, it was built in a triangular shape with eight batteries. It was expanded in 1657 and 1753, and later renamed after King Felipe IV of Spain.
The fortress is incredibly large and completely unlike any other Spanish fortress in Latin America. There doesn't seem to be much of a plan to it which makes it more ingenious and perplexing.
The defense system after the expansion of the fortress made it impossible to capture. Each battery and parapet protected one another, which means the entire defense system had to be defeated just to take one battery. In addition, extreme heat, humidity, and the threat of malaria from the mosquitos in the swamps near the castle made the conditions for both attacking forces (and Spanish soldiers) unbearable.
The complex system of tunnels, many of which have yet to be excavated, made it easy to hear the footsteps of enemies and for communication between Spanish soldiers.
Give yourself a good hour and a half to two hours. We recommend getting the audio guide to help understand it better, and don't forget to bring plenty of water. The fortress is about a 20 to 30 minute walk from the old city or a short taxi ride.
Visit Castillo San Felipe with Paisadventure on any tour that passes through Cartagena, or add Cartagena to any customized tour.