This is a Castle just outside the Walled City. It is a fortress built in the 1500’s to protect the city of Cartagena from invaders. It’s about a $5 cab ride here from the Old City, an about $20 to get in the castle. We went here on our last day and realized we should watch the sun set at Cafe Del Mar and took off. So we didn’t get to see much of the castle. However what we did see was amazing. The sun was starting to set as we arrived. The castle would also be a great place to watch the sun set.
To get to this island you will need to go by boat. The website provided is a well reviewed tour guide that will take you and bring you back to the island.