Las Bovedas was part of a prison that was built inside the walled City in 1792. It is now a series of tourist shops with various goods being sold. What attracted me to this area was the vibrant yellow color and the shaded interiors. It is a very cool area to walk around in and if you proceed to the end you will have access to climbing some of the City walls.
If you succumb to a guided tour of Cartagena it is likely that your tour guide will take you shopping for emeralds since the city is known world over as the place to buy them. Unless you know precious stones very well I would be very careful where you buy emeralds. The tour director of the tour I was on swore and had significant documents that he claimed the two stores he had sold the best emeralds at the best price.
You will also find several street merchants selling emeralds. Again beware!
According to several sources including several folks on Trip Advisor one place that tourists have great success buying high quality emeralds at reasonable prices is Joyeria Caribe. It is off of St. Martin and the address is; CLL 5a No 2-51 BOCAGRANDE.