Sometimes I'm brash when I travel, but I admit now that no one listens to me. For starters, all the cities in Colombia are safe, but going into a low demographic neighbourhood looking like a tourist with a backpack and camera in hand, is not the most recommended. You never know what the hundreds of eyes that are looking at you are thinking. I guess the fact of it makes you more afraid than what you'll feel like when you're there. Medellin is in a valley and a large part of the city was built on the slopes of the mountains so the underground train doesn't reach everywhere. The solution to this problem is to go by cable car (metrocable).