Switzerland. Not quite Niagara Falls but still well worth the visit.
The falls were formed approximately 14,000 to 17,000 years ago, during the last ice age, by erosion-resistant rocks narrowing the riverbed.
The falls are 150 m (450 ft) wide and 23 m (75 ft) high. In winter, the average water flow is 250 m³/s (~66,000 gallons per second). In summer, the average water flow is 700 m³/s (~18,500 gallons per second).
The falls even come complete with two small castles. Well, really more restaurants than castles. The medieval Schloß Laufen is over 1,000 years old and sits on the top of the north bank overlooking the falls.
Schloß Wörth sits on the south bank of the Rhine. Again, more tourist restaurant than castle.