COLOMBIA // Having pierced the rind of Las Murallas (the city walls). an explosion of tangy citrus colours confronts you in Cartagena's Old Town, on the Caribbean coast of Colombia. Cartagena's sturdy walls are a direct legacy of the visit, in 1586, of one Francis Drake, who invaded the Colombian city on behalf of Elizabeth I and stripped it of pretty much everything he could make off with. In the aftermath of the attack and occupation, the city concluded that it needed better defences. Once you're in the walled town, the best way to explore the historical districts of El Centro and San Diego is simply to meander, tasting local