Columbia is beautiful. I recommend going to Cartagena. The historic part of the city is gorgeous. The countryside is incredibly lush, the coffee is better than you can imagine, and you can get a great deal on emeralds. Like others have wisely stated, be smart about where you go, keep your guard up, stick to well traveled areas at night (as with any big city) and you should be fine. Expect customs agents to give you a little more attention on your return trip home than they would if you were returning from a place like London or Paris(expect them to ask take a peek through your bags), but as long as you aren't bringing back anything you're not supposed to, you're not going to have any problem.