If there is one city that any Colombian could recommend to a prospective tourist, it would be Cartagena. It's full of culture, fusing the old and the new.Not only that, the city is also nearby the Baru and the Rosarios islands, whose waters are laid with magnificent coral reefs that you will surely want to see.
These are all possible with Decameron Tours.
Link: Local Activities & Tours in the Hotel Decameron Colombia