Even in a hemisphere full of spots with unique appeal to visitors, Xochimilco in Mexico’s Federal District (about an hour from downtown Mexico City’s main square, the Zócalo) can claim a special place.An Aztec town dating back to the 10th century, today Xochimilco (“field of flowers” in the local Nahuatl language), it largely has the feel of a Mexico City suburb it's become, but with one major exception, for which it is justly famous: its 170-square kilometre (66-square-m