All I had known about this country even a year ago is cocain and Pablo Escobar. While being in Central America I met a lot of travelers who had been absolutely amazed by this country and I'd decided to learn more about its culture, history and situation nowadays. First on internet. After some research I'd decided that I want to visit it, since I was going to be in Panama and it's quite close, and flights are not expensive, and I've never been to South America before.
After couple months in Central I was quite tired of touristic places, so I decided to skip the coasts and concentrate on big cities.
The first one I arrived to was Medellín. By the way in Colombia I first tried Couchsurfing (my Couchsurfing experience deserves the separate article, I've started to write already). That's a magic place. And its main magic is that for some reason which you don't realize, you don't want to leave. Seriously, I've spent 3 weeks there and I can't even say what I was doing there for all this time. When I arrived I saw the ordinary city, nothing special. I couldn't understand why all the travelers love it so much. Now I'm quite sure that the main reason is people. They are very kind, helpful and positive. They make you feel very comfortable. You really feel you're welcome there.
The only thing I'd strongly recommend is a free walking tour. Well, it's not really free, they ask for tips after. They even tell you the approximate amount they expect to get from you (7-12 USD), but it's up to you, how much you give them, of course. There is only one company that organizes those tours. You should book them on the website in advance (1-1,5 day before). It lasts 4 hours and it's very interesting, funny and educational.
All the other things there are optional, in my opinion. Depend on your interests. As the second largest city in Colombia (after Bogotá, the capital), Medellín has everything.
The second city I visited was Cali. I went there only because they call it "the capital of salsa" (the dance) and I love to dance salsa. In general, I was disappointed. They have salsa parties everywhere, hundreds of it, but those parties I experienced in Medellín were much better. After all, quality matters, not quantity. So, though there are less parties in Medellín, I think for salsa you should stay there.
But there was one place in Cali I really enjoyed visiting. The museum called Caliwood (I wrote about it here: https://www.facebook.com/in.specter.photography/?ref=aymt_homepage_panel). And the Museo la Tertulia is quite nice (art museum) but everything is in Spanish there. So, Cali is worth visiting, but it's nothing to do there for more than 3 days, in my opinion.
The last city I visited was Ipiales. It's on the border with Ecuador. I spent there just half of the day. Not even in the city, I visited Santuario de las Lajas, the church built on the bridge over the abyss about 5 kilometers from the town. It was definitely worth it. It's the place you don't want to leave.
After that, I headed to Ecuador.