Here in central Mexico, the Gallinas River spills into the Tampaón River gorge to create Tamul waterfall, renowned as a jewel of the country"s wilderness. Both rivers offer great swimming near the falls, and boaters can float by on the Tampaón for close-up views. Both activities are best attempted between July and October, though: During wetter months, the falls converge into a thundering cataract as the Gallinas rises to form torrential rapids.