The Soo Locks allow ships to travel between Lake Superior and the lower Great Lakes. They bypass the rapids of the St. Marys River where the water falls 21 feet. These series of gates have been referred to as one of the great wonders of the world and it is still the largest waterway system on earth. No trip to Sault Ste. Marie is complete without a Soo Locks boat tour! They just closed up the tours for the winter last week, but they will open again in May.