Locks 4, 5 and 6 form the twinned flight locks that carry ships through the steepest part of the canal's route across the Niagara Escarpment. Working in sequence, the three locks together raise or lower a vessel by roughly 42 metres, doing the job of three ordinary locks stacked back to back. The 'twin' design places two parallel chambers side by side, so upbound and downbound traffic can move at the same time instead of waiting in turn.
For visitors, the draw is watching enormous lakers and ocean freighters inch upward as huge volumes of water flood in beneath them. The locks lie within the City of Thorold, and the adjacent Lock 7 Viewing Complex together with the paved Welland Canals Parkway Trail offer free vantage points to take in the spectacle up close.
