Designed by Antonio de Arévalo in 1639, the Fort of St. Philip's steep-angled brick and concrete battlements were arranged so that if part of the castle were conquered the rest could still be defended. A maze of tunnels, minimally lit today to allow for spooky exploration, still connects vital points of the fort. Notice the near-perfect acoustics in the tunnels here: Occupants could hear the footsteps of the approaching enemy. The climb is strenuous, but you'll be rewarded with some of the best views in Cartagena. Plan to get here by taxi—and expect to pay about 12,000 pesos one-way.
Av. Pedro de Heredia at Carrera 17, Cartagena, 130001, Colombia