Marching Powder is the biography of Thomas McFadden, a british cocain trafficker which got caught and sent to San Pedro. He describes his time in this super corrupt prison complex. Where you have to buy or rent your own cell in one of the different sections which act as kind of neighbourhoods. Having its own little economy. With little tiendas and restaurants, run by inmates and their families which live with them!
Later on Thomas starts offering tours to backpackers by bribing some of the guards to allow non-family visitors. Some come for the stories but for many the cheap coke, produced in San Pedro itself, is the main attraction. Many of these visitors end up staying over night and he even got a tourist girlfriend which lived with him for a while!
Read more about it for example here, Mike's Bogota Blog