During one our first days in Cartagena, we visited Castillo San Felipe de Barajas. We learned on our audio tour that the construction of this fortress started in 1536, but it was very advanced for its time. The fort was designed so that if it was attacked by the enemy, the Colombian soldiers could still defeat them from within. This impressive structure was attacked on several occasions, but never conquered.
The Cartagena heat was magnified as we explored the castle made of stone, so walking down into the maze of underground tunnels was a much-needed break from the sun, as well as one of the most interesting features.