Latest innovation from tourism offers trips with a social mission to travelers who want more from a holiday than sea & shopping. This summer, vacationers can pair a visit to the colonial Colombian city of Cartagena with an program aimed at raising awareness about the modern slave trade. [...] "I have been asked whether the tour, given its theme, was 'depressing,' " Karen Weiss, who took a similar trip to Thailand, explained. "I assure you that it was not.