Directions to find two major monger areas: MAYORISTA and CARRERA 53
MAYORISTA Metro: Ayur.
'Mayorista' (in terms of mongering) is a strip of cheap bars and brothels within walking distance of Ayur Metro station. Safe.
You can use a bus or taxi, or take the Metro in the direction of "El Estrella. " Ayur is the stop after Aguacatala. The Metro is also modern and safe.
As you get off the Metro you have to turn right along the station platform to exit ('saida' This takes you up some steps and you turn left at the top. You can see Mayorista area on a map before you leave if you like. It's on the opposite side of the Metro line to Poblado and the same side as Olaya Herrera domestic airport. The Metro bridge takes you over the freeway and the river. You can see the big Chevrolet / Autolarte building. It comes out onto a big dual-carriageway street, Calle 85, running at right angles to the Metro line.
Follow this street, Calle 85, staying on the same side (left hand side as you walk away from the station; the Chevrolet building is on the right hand side). You will pass the usual motley collection of street vendors selling street food and knicknacks.
Within a few minutes you reach the entrance to "Plaza Mayorista" which you ignore. Plaza Mayorista is an enormous covered wholesale market, warehouse area, about five enormous supermarkets, many small shops selling lots of things other than chicas. Nice clean place to eat and wear yourself out walking.
Ignoring the entrance to Plaza Mayorista, carry on along Calle 85. You pass the Terpel garage on your left. Set back from the road is the long Mayorista Plaza building (about 8 floors with a stripe of reddish brown brick along the middle). At the end of the block is a Plaza exit with a fancy silver canopy and some little waterfalls. Again ignore this and carry on along Calle 85. There's a barbed wire topped metal fence running along the Plaza area. Eventually Carlle 85 becomes something more 'normal' with small shops and bars and clubs and cafs and hotels cheap and less cheap. The chicas litter the pavement inviting you in. It winds up around Carrera 52. Choose well. Plenty of buses and taxis from here.
CARRERA 53 Metro: Parque Berrio.
This is definitely for the more adventurous and street-wise. Very cheap indeed. A block or so of cheap bars, clubs, stripshows with chicas spilling onto the pavement. Dangerous? Only for the foolhardy really, but the surrounding area is not that clean and lovely, especially at night, so investigating daytime first is recommended so you know your way around the area. Once in Carrera 53 you are reasonably safe if you are street-wise. You can watch a stripshow, no charge, though they like to collect a small amount after you've watched. There are many cons, but it is not like the rougher area of Prado or the almost adjacent Plaza Botero. However, you probably have to go through the rougher part to get to it. I suggest getting to know your options for getting back to the Metro or finding a taxi (ie Walking: any street that is well lit and has people. If in doubt, the big street going back to Parque Berrio Metro (Calle 51) is a good bet. However, Calle 53, while less savoury, is quicker for finding taxis (skip past the glue-sniffers etc).
This is an interesting area. The Carrera 53 chicas are 24/7 although there is a big difference between a morning on a holiday day and an evening towards the end of the week. Adjoining streets have interesting markets (the normal sort, not like Mayorista), architecture, museums, a stunning mall and plenty of cheap places to stay. Relatively gringo-free and you can have good fun. You should know how to laugh off the occasional malandro. Normal warnings in triplicate.
Carrera 53 (the chica part) is a block or two from Plaza Botero. The easiest way to find it is to go from Parque Berrio Metro to the Botero Plaza and Museum of Antiquities (a few yards in the direction of Prado, but opposite side of the tracks to Candelaria). When you get to the Plaza, the Museum of Antiquities is facing you as you face away from the Metro line. Just follow the road on your right-hand side (Calle 53) that goes past and the Museum, and turn left into Carrera 53 chica-walk.