It was truly impregnable and was never taken, despite numerous attempts to storm it. A complex system of tunnels connected strategic points of the fortress to distribute provisions and to facilitate evacuation. The tunnels were constructed in such a way that any noise reverberated all the way along them, making it possible to hear the slightest sound of the approaching enemy's feet, and also making it easy for internal communication.

This fort is a magnificent feat in engineering for its time, built in order to repel attacks by land of the English Crown. It takes a pinch of courage to visit its underground passages, sentry boxes and chambers where food and munitions were stored.

Some of the tunnels are lit and are open to visitors – an eerie walk not to be missed. Take an audio tour (COP$10,000 in English) if you want to learn more about the curious inventions of Antonio de Arévalo, the military engineer who directed the construction of the fortress.

The fortress is a short walk from Getsemaní, but if you're in a hurry a taxi costs COP$6000. Entrance is free the last Sunday of every month between February and November.