Visit the Rosario Islands. These islands are located 100 km off the coast of Cartagena. There you can sunbathe on unspoiled beaches, swim and snorkel in the azure Caribbean, and relax! Arrangements to visit these islands can be made through Trip Advisor.
Take a 10 minute boat right to a small island off Cartagena. Danny and I did a day trip here that we booked through Tripadvisor! We highly recommend it, it has the best view of the city, delicious resturant, and white sand beaches. There is also a hotel on the island if you want to spend the night!