This thundering natural wonder is located on the Niagara River and is shared by both Canada and the United States. It actually consists of two waterfalls. Ontario's Canadian Falls, (also called Horseshoe Falls) is actually bigger than the American Falls and sends nine times more water crashing down its edge. Both are more than 180 feet high. Millions of people visit the Falls every year. (ALAN SMITH—GETTY IIMAGES)