We visited Columbia and Cartagena as a stop on a Princess Panama Canal cruise.  We did a full day ships excursion that started at a Monastery on the top of a mountain that is part of the city center.  Then we visited the old fort that protected the city years ago. That was followed by a walking tour of the old city and then a couple of stops in the new city on the Peninsula. Very interesting city and worth stopping at. It felt completely safe in 2008.