I went to Colombia for the first time in 2008, spent 2 months there before going to the Dom Rep, went again in 2012 and got back in January after spending over a year and a half living there. I travelled a bit for the first 2 months then settled in Cali (supposedly the 13th most dangerous city in the world) and made a circle of colombian friends had a shower of pretty Colombian girlfriends and banged some whores
Learn Spanish and go, that's my advice
In fact you can get away without speaking Spanish but you will have 500% better time if you can manage something. Don't listen to the media reports, don't listen to people who go "oooOOOOOOOoooo Colombia is so dangerous" most of these people haven't been and are simply repeating things they've heard. You get some people who say it's really dangerous that have been, but if anybody who's been and is pushing the point they are likely to be the kind of swaggering douchebag that are trying to look tough and dangerous for having been to such a "violent" country.
The country is a lot safer than others I have been to in Latin America for example Bolivia or certain parts of Peru. In the entire time I was there only once did I have a run in with a knife gang who stuck me up for what was in my pocket, and that was in all the time i have ever been in Colombia. That's not to say it's not dangerous, there are certainly parts that are - but those are parts where you wouldn't really be going anyway - like some of the rural areas down south and up near the venezuelan border where the guerillas and FARC still hang out. Even at that FARC members will probably most likely get photos with you rather than kidnap you these days unless you are a politician, stinking rich or work for the American government.
Bogota however has got worse since I was there in 2008 - a lot more homeless and crack heads on the street after dark - avoid walking around Centro and La Candelaria after dark - best not to walk around alone or in twos late at night, try and go in a group but keep low key. Medellin is a lot nicer than Bogota, on a par with large European cities I say, a truly amazing city you will have a fucking blast
Just take care - the same goes for any city anywhere whether there or in Europe - just be street smart, don't flash jewellery, don't be overly loud and drunk in the streets, it ain't Magaluf. Whatever you do don't walk around in board shorts, fucking flip flops and sunglasses in a group all stretched out horizontally and sauntering along the pavement without a care in the world, blocking locals from getting past you, like I have seen tourists from Australia, the states and here do - you'll stick out and look ridiculous. You might be able to get away with a bit more in Cartagena where tourists are over everything, and of course San Andres, which basically is 60% Colombian tourists all year round.
With regards to mongering, in Bogota you have "la piscina" huge knocking shop with a pool in the middle of it, a bit like a nightclub. Girls in G strings and heels walking around like in the termas's in Brazil. Medellin, again you have similar places and again in Cali. Prices range from 50,000 pesos to I'd say around 150,000. You get what you pay for, although whilst in San ANdres I did pump some lovely girls for just 50k in "bar elefante" 50k is about 13 or 14 quid. I got myself onto the mileroticos website, be sure to google mileroticos colombia and there you will find a plethera of "prepagos" - prices vary. Another gold mine, is colombiancupid a dating website. It's full of every kind of colombian chick you will meet, tons of young stunners I dated literally dozens of girls off this, and got laid lots of times from gorgeous normal colombian girls not whores. Yet another goldmine is myfreecams, if you filter your search results to include just latin america, most of the girls are from colombia - you pay 20 bucks to get 200 tokens to start with which upgrades you to a premium membership which means you can private chat with the girls. My trick was tip them around 10 tokens to say hi, then just chat and chat and chat with them on cam, once they see you are not ancient fat and ugly, PLUS in their city many of them will be up for meeting you. 50% of the time I had to pay just like a normal WG, the other 50% was completely free - there are many girls on there who will jump at the chance to go out with a european guy as they find us exotic. Some of my girlfriends from Cali I met on this site, and we dated, we fucked again and again and they never asked me for a single peso. So yeah, learn some Spanish, it goes a long way
Hope I've been of help dude, anything you want to ask, ask me here or PM me and I'll give you the low down and help you out