The Trent-Severn Locks should be called the "Eighth Wonder". They vary from simple locks to "bath tub" and "railway car" locks.

When there is a great difference in elevation at a given location, hydraulic lift locks are employed. These "Bath Tub" locks work on a simple principal; there are two columns of water which act as hydraulic pistons which hold the two "bath tubs" up. When one bathtub has more water than the other does it will go down forcing the water into the other piston causing its basin to raise. When it reaches the top, the boats are able to continue into the higher body of water.

Here we are in a tub waiting to go up along with a few other boats and a paddle wheeler tour boat. 

Here is the view after the tub got to the top.