I was recently in Cartagena and Santa Marta, I'll tell you below to visit tourist sites in these 2 places: You can make these tours yourselves, it is much cheaper in these 2 places and is safe.
I recommend as the first attraction visit the Castillo de San Felipe de Barajas Cartagena. This castle is the biggest strength that the Spanish built centuries ago throughout Latin America is vast, from the top you can see the whole city of Cartagena with very nice view (inside the castle you will find tourist guides, local crafts, museum, etc. ) value $ 8 dollars entry. A seaport taxi to the castle can cost about 5 dollars. In visiting you take an average of 2 to 3 hours, I recommend buy water or liquid before entering, there are vendors outside sell you bottled of water (1 dollar costs the bottle) This site is secure from theft. Then you should visit the walled city. This small city is in the center of Cartagena surrounded by fortress for centuries, will find a rich man in cultural history of the events that happened about 4 centuries ago, the streets, colonial homes and sites that used the Spanish government at that time, in find currency exchange houses, restaurants, shopping items from Colombians, bars. Visiting the site can take about 2 to 3 hours at the entrance to the place you can buy a map of the area. This site is secure of theft. Do not have any cost to enter this site. A taxi from the port at the entrance of this place will cost $ 5 dollars, tell the driver to drop you at the clock tower (is the official entry). If you have time you can go to BOCAGRANDE BEACH. This site is near the walled city about $ 5 dollars taxi ride from the port or 3 dollars from the clock tower (city´s center). On this beach you can swim without any danger of insecurity because this area is surrounded by many 4 and 5 star hotels, banks, restaurants, bars. This is the place where tourists stay mostly in Cartagena. They are also the Rosario Islands from the city of Cartagena take a boat it will cost about 10 or 15 dollars to the islands with crystal clear waters for snorkeling, diving, and there are also 4 and 5 star hotels in some of the islands, these are close Cartagena city you can take the boat or obtain information near the clock tower at the walled city, or Bocagrande beaches. There are other places to visit include the Museum of Gold, purchase Colombian antiques at the vault´s it is near at the clock tower, the Popa´s convent, Malls with air conditioner. Also from Cartagena departure tourist sailboats that travels to Panama safely it costs around $ 300 dollars, 3 days traveling time and take you to paradise islands in Panama which is the sector of San Blas is an archipelago of islands in a chain attached around 300 islands with crystal warm waters.
IN SANTAMARTA: there are 2 alternatives:
The city of Santa Marta´s beach only to enjoy walking (not to take a bath because some boats throw gasoline and garbage to the sea), then walk 100 meters will find the downtown to visit the Gold Museum, visit the oldest church built by the Spaniards in Latin American, buy Colombian antiques, the Center (business area) and the beach is near the port, a $ 5 dollars taxi ride, and if you have some time visit a nice place: La Quinta de San Pedro (St Peters Ranch) $ 5 dollars entry, rich in South American history. In this place there are several museums, parks surrounded by trees, flowers and a large farm house in which was habited and died Simon Bolivar (the freedom man), here you will find guides that will take you around the place. (For people who do not know who was Simon Bolivar, he was the legend who freed 5 nations from the Spaniards about 2 centuries ago where Spaniards lost these territories in bloody battles where many people died on both sides, countries that Bolivar freed were: Colombia , Venezuela, Ecuador, Peru and Bolivia) a taxi from downtown to this place should not cost more than $ 10 dollars, although there is public transportation for 1 dollar but I recommend to take taxi. If you are looking for a beach there is a nice one called Rodadero Beach 15 minutes by taxi value 10 to 15 dollars from the port, or from Santa Marta´s downtown you can take public transportation costs $ 1 dollar per passenger but the driver only receive Colombian peso, it takes 15 to 20 minutes to Rodadero beach. This place is a small town touristic and safe, there is a good clean beach for bathing, rent kayaks for $ 5, water bicycle rent for $ 5 per person, rent bicycles and ride along the rodadero streets, banana boat, beach tents and seats.This place is surrounded of tall buildings, excellent hotels (5, 4,3 stars), good restaurants, and good place to buy Colombian antiques, its´s a safe place to walk on the area. From this place can take you by boat to different beaches around 5 minutes on boat, example (the white beach) for $ 10 a person. Rodadero on the beach there are several tourist agencies that take credit cards as payment which will lead you to endless beaches and cultural sites of the indigenous tribes of the sector. If you are staying several days I recommend you take a tour to the LOST CITY in the Sierra Nevada de Santa Marta, where indigenous cultures like (Tayrona, Wayu) lives for centuries, also in this area find beautiful beaches, clean fresh water rivers where you can take a bath. The Tayrona´s National park located in the Sierra Nevada de Santa Marta which it means (Range of mountains and volcanoes of Santa Marta) these chain of mountains are the highest in the world in terms of its proximity to the sea which is full of clear fresh rivers of many which end at the sea, rich in forest and wildlife, indigenous cultures (Mountain´s highest peak is 5700 meters above sea level) Any other question can make to me my email