Niagara Falls has the Maid of the Mist. Iguaçu has Macuco. I know which one I'd choose. Macuco participants pile aboard 8m (25-ft.) zodiacs, the guide fires up twin 225-horsepower outboards, and you're off up the river, bouncing over wave trains, breaking eddy lines, powering your way up the surging current until the boat's in the gorge, advancing slowly toward one of the (smaller) falls. As the boat nears, the mist gets thicker, the roar louder, the passengers wetter and more and more thrilled (or terrified), until the zodiac peels away, slides downstream, and hides in an eddy until everyone's caught his or her breath. Then you do it all again. Allow 1 hour for the entire trip.