Caribbean archipelago off the coast of Colombia
Islas del Rosario is an archipelago located in the Caribbean Sea off the coast of Colombia. Since 1988 the archipelago has been protected as a national park, encompassing a total area of 120,000 km.
The Islas del Rosario are approximately 100 km (62 mi) from Cartagena, reachable by a 90 minute boat ride. Activities include swimming, fishing, snorkeling, and visiting the aquarium.
Regardless of what mainstream guide books tell you, the cheap tours to Isla del Rosario have nothing to do with appreciating nature nor having a good time on a nice beach. Tours from Cartagena cost between COP$50,000 - 70,000, including boat transport and lunch at Playa Blanca. You will be dropped at an island to visit the aquarium or go snorkeling (for an extra cost), if you don't want to do either, you will be left in a very small area having nothing to do, waiting for the others for an hour.
Food and drink are more expensive than the mainland and expect to pay for bathrooms and change rooms.
In Cartagena, several agents arrange boat tours to Islas del Rosario. The tour usually includes lunch, a visit to an aquarium, and a few hours at Playa Blanca. Not included in the price is the harbor tax and park entrance (COP$16,500 total - July 2018) and the entrance fee to the aquarium (COP$15,000).
The tourist offices in the center of the old town are a good place to compare the many tour options. If you buy your tour at one of the street vendors, don't pay in advance, preferably pay part or all upon return to Cartagena.
At least one of these tours is to a resort "Coco Liso" which is something like a Colombian butlins. You will be promised a beach, pay a high fee, then disembark a boat after an hour and a half to be greeted with a fairly basic hotel, gimmicky pool, and about 6 ft² (0.56 m) of beachfront. If you befriend a local upon arrival to the island, they might lead you to their private beach - quite beautiful, and all the more interesting for having its existence totally denied by the tour operators.
There are several island groups within the archipelago:
Beer price COP$5,000 - 6,000
Cocktail price COP$15,000 - 20,000
Potato chips COP$7,000
Bring your own snacks if necessary.